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RELOADERS CORNER: Velocity Consistency, Part One

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Shot-to-shot muzzle velocity consistency is almost always a high-ranking goal for the handloader. But what about when it’s just awful? READ MORE

chronograph display

Glen Zediker

Last edition the topic was a wide-scope look at propellants, and the underlying point was how to get started, how to choose one. There’s not a perfect answer to that, or not one I can warrant as absolutely decisive.

Propellant choice often comes down to experience (good and bad), and that’s one reason that many of us, and me most definitely, tend to stick with a few, and those also are the first we’ll try when starting up with a new project. It’s also one reason we might be hesitant to try a propellant again if it didn’t work well the last time. I have those hesitations.

There are also criteria that we’d all like to have met, and, as also said last time, sometimes those have to be ranked or weighted. We may not find the maximum velocity with the smallest group size with one propellant, and, for me, group size gets the most weight. That’s why I said that the best choice is often the one with the fewest compromises, and that’s assuming there’s likely to be some compromise, somewhere. And that’s a fair and wise assumption.

One criteria that I and others have pretty high on our lists is velocity consistency. One measure of a “good load” is low variations in measured muzzle velocities. This, without a doubt, is of more importance the more distant the target.

The propellant that tested showing the lowest shot-to-shot velocity deviation does not necessarily mean that load combination is going to be the most accurate. One reason it’s important might not only to do with on-target accuracy as it does with providing clues about either the handloading protocols we’re following or the suitability of the component combination we’re using.

This article will focus more on that last — suitability of the component combination — and more to follow later will be dedicated to the performance component of consistent velocities.

I got a letter just before doing this article asking about reasons for seeing high velocity deviations. This fellow, a loyal reader of my books, was using the same component combinations and tooling advice I take myself and also publish, and not getting good results. As a matter of fact, his results were horrid. He was seeing deviations, shot-to-shot, in the vicinity of 100 feet per second (fps), plus. That’s huge.

After much time spent testing all this to collect enough notebook entries to think I have some handle on it, a half grain (0.50 gr.) of propellant in most small- to medium-capacity cases (say from .223 Rem. to .308 Win.) is worth about 40 fps. Given that, 100 fps difference is not likely to come from a propellant charge level variance.

Another reader posted a comment-question last article here regarding how to know if aged components were still good, still performing as they should, and this is a place to start looking if we’re seeing radical inconsistencies.

Two questions at the same time, as I’ve said before, usually point me toward a topic.

Moisture is the enemy in propellant and primer storage. The “cool dry place” is hard to come by, around these parts anyhow. I’ve had propellant go bad after having been stored in resealed containers. So far, I haven’t had any lose its potency after many years of storage in the factory-sealed containers.

“Go bad” can mean at a couple of things, by the way. One is that the propellant ages to the point that it changes. If propellant “spoils” it smells bad! It will have an acrid aroma. Don’t use it. Another way it goes bad is pretty easy to tell: it clumps. That is too much moisture. Don’t use it. Put it out in the garden, it’s a great fertilizer — honest.

Primers? It’s hard to tell… Bad primers still appear good.

My letter-writer’s huge velocity deviations were solved by a change of primer, and, mostly, a box of fresh primers. I kind of knew that was the component-culprit because he was having the same results or effects from different propellants.

Primers should be stored in air-tight containers, which will be something other than the factory packaging. Primers are “sealed” but that’s a lightweight assurance. Touching them, for instance, won’t hurt them, contrary to rumors, but more prolonged exposure to excessive moisture can and will take a toll, and its effects are very likely to be as inconsistent as the performance of the compromised primers.

Another strong caution: Always remove, or never leave, however you prefer, propellant in a meter. After you’re done with the loading for the day, return it to its storage container and cap it back tightly. Same with primers. Any left over in the priming tube or tray should go back to safe storage. Clearly, this all has a lot to do with the environmental conditions of your loading-storage area.

Out of curiosity, I filled a case with some small-grained extruded propellant and left it sit out in my shop. It was clumped when I checked it next day (24 hours). I had to get a pipe cleaner (nearest handy tool) to get it all out of the case. I don’t store propellant or primers in my shop, and that’s the reason… Yes, we have some humidity in my part of the world.

Excluding those obvious issues, what makes some combinations produce higher or lower velocity consistencies takes some experimentation to improve (or give up on).

Sometimes (many times) this all seems more like art than science. It is science, of course, but it’s not tidy; it can’t always, or even often, be forecast.

I’ve seen the biggest effect from a primer brand change. I also, though, don’t swap primer brands around each time I do a load work up and the reason is that there are other attributes I need from a primer. Since I’m loading nearly always for a semi-auto, an AR15 specifically, I have to use a “tough” primer, and that also means one that will accept near-max pressure without incident.

Point is that if you’re running a rifle/ammo combination that isn’t limited by either propellant choice or primer choice, you might very well see some influential improvements by trying a different primer (after getting the propellant decided on). Do, always, reduce the charge at least a half grain before using a different primer brand — primer choices also decidedly influence velocity and pressure levels. Again, in my experience, more than you might imagine.

Next time, more about the performance component of consistent velocities, and a whopping lot more about how to improve that.

Check Midsouth storage solutions HERE

The preceding is a specially-adapted excerpt from Glen’s book Top-Grade Ammo. Available HERE at Midsouth Shooters Supply. Visit ZedikerPublishing.com for more information on the book itself, and also free article downloads.

RELOADERS CORNER: Gas Port Pressure

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It’s not always possible to separate guns from loads, and there are some important things to know to get the most from your semi-auto. Here’s one! KEEP READING

casing in air

Glen Zediker

I have spent the last couple of segments taking a big step back recollecting my own (early) experiences and education as a handloader. Hope you’re happily indulging me, and hope even more that there’s been some good ideas that have come from it.

I started reloading as a matter of economy, and because I wanted to shoot more. Said then and said again now: if the impetus for reloading is saving money, you really don’t save money! You just get to shoot more for the same cost. Hope that makes sense, and likely you already understand that. Clearly, there are other reasons or focuses that attract folks to handloading, and personalizing ammo performance, improving accuracy, are leading reasons.

I’ve been at least a tad amount (to a lot) biased all along in my department topics toward loading for semi-automatic rifles. That’s been done for a few reasons, and the primary one is that, no question at all, there are specific and important details, a lot of dos and don’ts, in recycling ammo for a self-loader.

This is the reason I’ve been careful to specifically point out the “semi-auto” aspect of any tooling or preparation step. I’d like some feedback from you all with respect to your motivations and applications in handloading. Why do you do it?

Another reason is that, and I know this from much input, as happened with me 45 years ago, my interest in learning to reload came with ownership of a semi-auto that I absolutely loved to shoot! Here of late, my plumber, for a good instance, proudly announced to me outside the local hardware store that he had just purchased his first AR15 and showed me the paper bag full of .223 Rem. cartridges he had just purchased there. A scant few weeks later: “Could you help me get together some tools and show me how to reload?” I did.

Back to the focus, finally (I know) of this topic: what are those differences comparing semi-autos to anything else?

There are a few points, but one of the first, and one of the most important, is component selection. Case, primer, propellant. Propellant first.

AR15 gas port
As .224-caliber bullets get heavier, there’s a tendency toward many using slower-burning propellants. Often, the slower-burning fuels produce lower chamber pressures, which means more velocity potential (that’s true with just about any rifle cartridge). But! Gas port pressure will increase with slower and slower burning propellants. Can’t have it all, and make sure “function” is first on the list. That’s safe and sane function, by the way, not “over-function!”

I’ll assume, pretty safely, that the semi-auto we’re loading up for is an AR15, or some take on that platform. If so, it will have a “direct impingement” gas system. That’s a pretty simple arrangement whereby the gas pressure needed to operate the system, which cycles the action, is bled off from the barrel bore via a port. From there it goes through a manifold and then into a tube, and then back into the bolt carrier via the bolt carrier key. Gas piston operation is more complex, but what’s said here applies there also respecting propellant selection.

So, it’s kind of a wave. The idea is to get the wave to peak at a point where there’s not excessive gas entering the system, but there is sufficient gas entering the system. Mil-spec. 20-inch AR15 calls for 12,500 psi, for what that’s worth. And “piston” guns are nowhere near immune from concerns about port pressure.

The burning rate of the propellant influences the level of gas pressure at the gas port, and this, easy to understand, is referred to as “port pressure.” The original AR15 rifle gas system component specs (20-inch barrel, port located at 12 inches down the barrel) were created to function just fine and dandy with 12,000 PSI port pressure. Much less than that and there might not be enough soon enough to reliably cycle the works. Much more than that and the operating cycle is accelerated.

Port pressure and chamber pressure are totally separate concerns and only related indirectly.

Rule: slower-burning propellants produce more port pressure than faster-burning propellants. As always, “faster” and “slower” are relative rankings within a variety of suitable choices. The answer to why slower-burning propellants produce higher pressure at the gas port comes with understanding a “pressure-time curve.” A PT curve is a way to chart consumption of propellant, which is producing gas, along with the bullet’s progress down the bore. It’s what pressure, at which point. I think of it as a wave that’s building, cresting, and then dissipating. Slower propellants peak farther down the bore, nearer the gas port. Heavier bullets, regardless of propellant used, also produce higher port pressures because they’re moving slower, allowing for a greater build-up about the time the port is passed.

RE15
I put the (very safe) cut-off at H4895 burning rate. I’ll go as slow as RE15, and have with safe success, but its influential differences are noticeable. I can tell you that a 4895 is well within the optimum range to deliver intended port pressure (“a” 4895, mil-contract variety, was actually the early original 5.56 propellant).

To really get a handle on all this you have to picture what’s happening as a bullet goes through the barrel in a semi-auto, and keep (always) in mind just how quickly it’s all happening. Milliseconds, less than a few of them, define “too much” or “not enough.” As the bullet passes the gas port, there’s still pressure building behind it, and there’s more pressure building still with a slower propellant. After the bullet exits the muzzle, the pressure doesn’t just instantly go away. There’s pressure latent in the system (all contained in the gas tube and bolt carrier) that’s operating the action.

The symptoms of excessive port pressure come from the consequence of a harder hit delivered too soon, and what amounts to too much daggone gas getting into and through the “back,” the bolt carrier: the action starts to operate too quickly. The case is still a little bit expanded (under pressure) when the bolt starts to unlock and the extractor tugs on the case rim, plus, the increased rush of gas simply cycles the action too quickly. That creates extraction problems and essentially beats up cases. They’ll often show bent rims, excessively blown case shoulders, stretching, and so on.

Getting gas port pressure under control makes for improved function, better spent case condition, and less wear and stress on the gun hisseff.

There’s a huge amount more to talk about on this whole topic, and a good number of ways to get everything working as it should. But. For this, the most a handloader can do, and it’s honestly just about the most influential help, is to stay on the faster side of suitable propellants. Without any doubt at all, there will be rampant disagreement with my advice: no slower than Hodgdon 4895. Most all published data lists propellants from faster to slower, so find H4895 and don’t go below it. That’s conservative, and there are a lot of very high scores shot in NRA High Power Rifle with VARGET and RE-15, but those are edgy, in my experience, and define the very upper (slowness) limit.

m14 gas system
This doesn’t only apply to AR15s. The M1A is VERY sensitive to port pressure, which is also propellant burn rate. It’s a gas-piston gun. Same cut-off on burning rate is advised for these: H4895. I sho learned this the hard way by dang near wrecking my first M1A: bolt stuck back after firing a dose of H4350. That was before I met Sgt. Jim Norris and got the lecture I’me giving you. Thanks Sarge!

That alone doesn’t mean all AR15 architectures will be tamed (carbine-length systems are particularly over-zealous), but it does mean that port pressure will stay lower, an important step.

A caution always about factory ammo: some is loaded for use in bolt-actions (especially hunting ammo(, and might bea very bad choice for your .308 Win. semi-auto. AR15s are actually fairly more flexible in showing clear symptoms, some no doubt due to the buffered operating system and overall mild nature of the .223 Rem. cartridge.

This article is adapted from Glen’s books, Handloading For Competition and Top-Grade Ammo, available at Midsouth HERE. For more information about other books by Glen, visit ZedikerPublishing.com

 

RELOADERS CORNER: Incremental Load Work-Up

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To get the most from your load testing, in the shortest time possible, learn the “Audette Method,” and put it work for you. Here’s how!

sight in target
Use a target that’s, one, easy to line up on, and, two, lets you make notes on the target itself. I usually circle and note the 3-shot increments, or you can add a number by each shot hole to indicate which try they belong to. Midsouth has some HERE

Glen Zediker

Last edition I suggested taking the step toward putting together a “portable” loading setup to allow for load development right at the range. This time I’ll talk about an idea on getting the most out of a test session in the quickest and surest way.

I have followed an “incremental” load work-up method for many years, and it’s served me well. Some call it the “Audette Method” named for the late and great Creighton Audette, long-time long-range and Benchrest experimenter.

Backing up a bit: Being able to employ this method efficiently requires having spent the preparation time, doing your homework, to know exactly how much “one click” is worth on your meter. Whether the meter clicks or not, it’s the value of one incremental mark on the metering arm. The value of that click or mark varies with the propellant, but by weighing several examples of each one-stop variation (done over at least a half-dozen stops) you’ll be able to accurately increase the charge for each test a known amount.

harrell's meter mounted
I count on a Harrell’s Precision meter. Its Culver mechanism allows for easy and accurate incremental adjustments in working up a load. The dryer sheet eliminates static electricity.

I usually test at 300 yards. That distance is adequate to give a good evaluation of accuracy and, for the purposes of this test, is also “far enough” that vertical spreads are more pronounced. Testing at 100 yards, sometimes they all look like good groups… So it’s at about 300 yards where we’ll start to see more difference in good and bad.

Get to the range and get set up, chronograph in place. Put up a target. Use whatever gives you a clear aiming point, but it’s helpful to have a light background not only to see the holes easier using a scope, but also to make notes on. More about that in a minute.

Use the same target for the entire session. (Put pasters over the previous holes if you want, but don’t change paper.) The reason for using the same target for the whole session is that helps determine vertical consistency as you work up through successively stouter propellant charges.

I fire 3 rounds per increment. As it gets closer to “done,” I increase it to 5 or 6. At that point I’ve hit a couple of speed points, two or three increments that represent a performance level I can live with (one is on the “iffy” end of the pressure, and I rarely choose that one) and am focusing more closely on group size. Final confirmation comes with one 20-round group. For what it’s worth, I usually pick the one in the middle.

A 3-round volley might seem inadequate, but it’s not if there’s confidence that the rounds are being well-directed and speed is being monitored. If I’m seeing more than 12-15 fps velocity spreads over 3 rounds, I’m not going to continue with that propellant. Same with group size: if it’s a big group over 3 rounds, it’s going to be a bigger group later on.

I’m sho no mathematician-statistician, but from experience I’ve found that, while certainly there’s some probability that the first 3 rounds fired might represent the extreme edges of the load’s group potential, and that all the others are going to land inside them, uhh, that’s not even a little bit likely. If it starts bad it finishes bad. On the contrary: no, just because the first 3 shots are close together and the velocity spread is low doesn’t mean it’s not going to get worse. Groups normally get bigger and velocities get wider, but, we have to start somewhere. It’s a matter of degrees. Also, the quality (accuracy) of the meter factors, and the better it is the better you can judge performance over fewer examples. And this is new brass, so that’s going to minimize inconsistencies further.

I can also tell you that it’s possible to wear out a barrel testing. No kidding.

Back to the “incremental” part of this test: As you increase the charges, bullets impact higher and higher on the target paper. You’re looking for a point where both group sizes and impact levels are very close together. If the groups are small, you won! That’s what Crieghton called a “sweet-spot” load, and that was one that didn’t show much on-target variance over a 2-3 increment charge difference (which is going to be about a half-grain of propellant). The value of such a load is immense, especially to a competitive shooter. It means that the daily variations, especially temperature, and even the small variances in propellant charges that might come with some propellants through meters, won’t affect your score. It’s also valuable to a hunter who’s planning to travel.

audette method loading
Audette Method: If it would only always work this way… This actually did work as shown so I captured and recreated it for posterity. The numbers on the left represent approximate propellant charge weights and the lines each indicate one click on my Harrell’s powder meter, a value about 0.15 grains of the propellant used in this test. Going up two clicks at a time for eight tries took me from 24.0 grains to about 26.0, which is a good range from a reasonable starting charge to pressure symptoms. I didn’t add in the velocities since that’s inconsequential to this illustration, but will say that “8” was too much and I settled on “6.” To make more sense out of this illustration, that ended up being 25.5 grains — step 6. I also went up using three rounds and skipping ahead by adding more clicks to the meter after viewing the (low) speeds on the first three groups (that’s why there’s no number 4 step; I went from step 3 to step 5). This has a lot to do with intuition sometimes. Point is, and should be, that here’s how the “Audette Method” is supposed to work: impact elevation on target goes up (these were fired at 300 yards) with charge increases, groups get smaller (hovering around two inches for this test) and stay small, and then elevation begins to stabilize. Choose a load that’s within this range. Then it’s a “sweet-spot” load. If this happens in your test, ask for no more!

That was the whole point to following this process. First, and foremost, it’s to find a good-performing load. It’s also how you find out if the propellant you chose is going to produce predictably. I can also tell you that I have chosen a propellant and a load using it that wasn’t always the highest speed or even the smallest single group. It was chosen because it will shoot predictably all year long. I base everything on the worst group, biggest velocity spread, not the smallest and lowest. If that doesn’t make sense it will after a summer on a tournament tour. If the worst group my combination will shoot is x-ring, and the worst spread is under 10 fps, it’s not the ammo that will lose the match…

As said to start this series, I started loading at the range because I got tired of bringing home partial batches of loser loads. And, you guessed it, the partial boxes usually contained recipes that were too hot. The only way to salvage those was to pull the bullets. Tedious. Or they were too low, of course, and fit only for busting up dirt clods. Plus, I’m able to test different charges in the same conditions. It’s a small investment that’s a huge time-saver.

If you do invest in a portable setup, exploit potentials. The possibilities for other tests are wide open, seating depth experiments, for instance.

CHECK OUT MORE TARGETS AT MIDSOUTH HERE

The information in this article is from Glen’s newest book, Top-Grade Ammo, available HERE at Midsouth. Also check HERE for more information about this and other publications from Zediker Publishing.

RELOADERS CORNER: Bullet Jump 2

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Tips that help take bullet jump out of the accuracy equation. Find out how!

leade
This is an aluminum staub cut with a chamber reamer. It’s easy to see the transition to the lands. The more smoothly a bullet enters the lands, the better it will shoot. When seating depth can’t be idealized, choosing a “gentle” bullet is the best defense against ill effects of jump.

Glen Zediker

Last time I shared some insight about bullet “jump,” and specifically with respect to the viability of setting up a “zero-jump” chamber/ammo combination.

To hit the highlights: Jump is the gap the bullet must traverse when it leaves the case neck to engage the lands or rifling. Generally, best (and better) accuracy comes with this gap is reduced to a minimum amount, or at the least reduced. Better is better.

To go farther into this topic, it’s worthwhile to move the bullet around, seating it more or less deeply (nearer or farther from the lands at rest) to maximize accuracy. Clearly, there’s a limit on cartridge overall length if the rounds have to fit into a magazine box so they can feed right. In NRA High Power Rifle competition, the AR15 pilots are specifically not allowed to have the rounds feed from the magazine in semi-auto mode; each round must be loaded into the chamber one at a time for the “slow-fire” segments, which includes the 600-yard event. That means competitive High Power shooters using AR-platform rifles are free to move the extra-long 80+ grain .224-caliber bullets out to near or on the lands when chambered. That doesn’t really matter but it explains the popular “Wylde” chamber we tend to use. It’s got a long enough throat to free more case volume and also provide a bigger “expansion chamber” for burning propellant gases, but it’s not as long as a NATO-spec so should perform better with bullets that do have to be loaded deeply in enough to fit the magazine box. Something like a Sierra 80gr or 82gr Berger won’t usually shoot worth a flip loaded to mag-length. That bullet, and others similar, are simply too dang long for a .223 Remington case. A huge amount of the bullet swallows up the case interior.

Sierra bullets compared.
It’s not all in the ogive specs, but it’s influenced by it, because those specs influence the overall profile of the bullet. Here’s a .224 Sierra 77gr MatchKing next to an 80gr MatchKing. The first is approximately 8 calibers, the 80 is approximately 12. The marks indicate the location of the first point of coincidence of land diameter. Considering the overall profile differences, it’s pretty clear that the 77 jumps with better results when each is loaded to the same cartridge overall length. There’s just 3grs difference in these bullets but they’re worlds apart in both tolerance and performance.

The best defense against ever worrying over jump, meaning whether you’re getting good accuracy regardless of the amount of bullet jump (well, at least within reason…) is bullet choice. Specifically, a tangent-profile bullet with a conservative ogive. Recollecting from some materials I did a while back, a “secant” profile is a sharper taper-in from bullet body to bullet tip; a tangent is a smoother transition. Secants, more or less, have a “shoulder” indicating a more abrupt taper rather than a smooth arc. For examples: true VLD (very low drag) and the Hornady A-Max are secant.

Bullets with relatively shorter nosecones and relatively longer bearing areas (length of the bullet that’s in contact with the rifling) are likewise more tolerant of jump.

Sierra 69, JLK 70 VLD
Here’s an example of different .224 bullet profiles at essentially the same weight. A Sierra 69gr MatchKing on left and a JLK 70gr VLD. The tangent 8-caliber-ogive (approximate) Sierra shoots great when it’s jumping; the secant 15-caliber-ogive VLD tends not to shoot well at all unless it starts touching the lands.

There’s been a trend for many years now toward creating bullets with higher ballistic coefficients. Worthwhile pursuit! Only issue is that when a bullet design features better aerodynamics, the features of that are, yep, longer nosecones with shallower angles. The ogive (what I’ve been more descriptively calling the nosecone because it’s easier to picture) usually is expressed in calibers. Technically it’s “calibers of ogive,” and that’s the ogive radius divided by the caliber. To me it’s easier to picture looking at the “other side” of the equation: the arc that scribes the profile in multiples of the bullet’s caliber. So, a 7- to 8-caliber ogive is a tighter circle (more rounded profile) than a 12- or 15-caliber ogive. Most of the “high-BC” profiles use a 15, some more. In other words, they’re stilettos.

calibers-of-ogive
Here’s an illustration of calibers-of-ogive from Sierra. That transition area from bullet diameter to first point of contact with the lands (which will be land diameter, and at least 0.005 smaller) has influence on how well a bullet endures jump. A lower-number is favorable in this regard. In this illustration the ogive radius, 2.240 inches, divided by the caliber, 0.308, gives 7.27. That should tolerate jump well.

I’m kind of breaking this down farther and faster than exercising good technical care in covering this topic should warrant, but: comparing both same-weight and same-caliber bullets, the longer it is the more sensitive it’s going to be to jump.

I have shot way too many high-X-count 300-yard cleans with bullets jumping 0.030+ inches to say that it’s not possible to have good accuracy unless jump is minimal. I admit that’s only a 1 moa group. I’m also using what some makers call a “length-tolerant” bullet, and specifically that’s a 77gr Sierra Matchking, and the same goes for a Nosler 77 or Hornady 75 HPBT (not A-Max). It’s the bullet form, not just its weight, that has the strongest influence on all this.

So, do you have to abandon better ballistics to attain better accuracy? Maybe. At least to a point. With the smaller calibers, which don’t have other advantages larger calibers have simply by virtue of weight and sectional density, there tends to be an effectively greater discrepancy between the lighter and heavier (again, it’s really shorter and longer) bullet ballistic performances.

A rifle with a generous-length magazine box provides greater jump-reduction via loaded round architecture. If there’s enough room, a bullet can be scooted out to the limit of the space within the box.

As always, well at least usually, there are tools! Get them and use them. A gage “set” from Hornady is well advised. There are others similar. I’ve been using their LNL Overall Length Gage and Bullet Comparator for many years and receive needed results. The first tool indicates the seating depth that touches the lands, and the second provides more reliable and accurate means to measure and record it.

Hornady LNL gage
This Hornady LNL gage pair gives you the tools needed to determine the jump you’re getting with the bullet you’re using. Check it out HERE

The leade, which, again, is the transition to the lands and determined by the chambering reamer (or throating reamer if custom-done) does influence tolerance for jump. The shallower the angle the better, but, that’s a two-edged issue. Take a commonly-used 3-degree leade and make it a more preferable 1.5-degree leade and that takes way on more than double the distance (length of cut) to attain. Again, when there’s a magazine getting in the way of bullet seating depth flexibility, a shallower leade eases transition into the barrel bore for a jumping bullet, but also increases jump. There are some cartridges, like David Tubb’s 6XC, that were designed specifically to “perfect” all these relationships: magazine-mandated cartridge overall length, bullet choice, and leade in, and it’s one reason it owns the records it does. Otherwise, it’s often a compromise… But don’t compromise accuracy for anything. A smaller group is, in the long run, the best defense against both wind and distance when it comes to hitting a target. Reliable feedback equals correct adjustments.

The preceding was adapted from Glen’s newest book, Top-Grade Ammo, available here at Midsouth. For more information on this book, and others, plus articles and information for download, visit ZedikerPublishing.com

RELOADERS CORNER: Bullet Jump: does it really matter? (Part One)

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The distance a bullet travels to enter the lands is a topic of much concern to the precision shooter. This series takes a look at why it matters, and also when it doesn’t…

Glen Zediker

bullet jump
Here’s jump: it’s the distance from the end of the case neck portion of the chamber to the first point the bullet will engage the lands or rifling.

Bullet jump: the open space a bullet must span until its first point of sufficient diameter engages the barrel lands.

Last week I had a long phone conversation with a fellow who had been bitten by two bugs, two somewhat conflicting bugs (at least seemingly so on the onset). The one was a regrouping equipment project for USPSA-style practical rifle competition, and the other was for a desire to maximize accuracy, which is to minimize group size. This fellow had been involved in competition long enough to decide to stay with it, and was re-upping his AR15 upper with a new custom barrel. He wanted to have the best accuracy he could buy, and that’s a worthwhile pursuit as long as there’s a budget that supports it.

The subject of bullet jump became the dominant topic.

Yep, he had read my books and a few others and developed the impression that minimizing bullet jump was one crucial component to maximizing accuracy. That’s fair enough. I’ve gone on about it, as have others. Adjusting bullet seating depth can make a big, big difference in shot impact proximities. However! The reason bullet jump matters — usually — is largely, almost exclusively, because of some bullet profiles being more finicky than others. Namely the longer and spikier “very-low-drag” type bullet profiles.

The first point of “major diameter” on a bullet is what coincides with the land diameter in the barrel. If that’s a .22 caliber with 0.219 diameter lands, then the first point along the nosecone of a bullet that’s 0.219 is the distance. Gages that measure this distance (Hornady LNL for instance) aren’t necessarily going to provide perfect coincidence with land diameter, but still provide an accurate bullet seating depth that touches the lands.

If you find the cartridge overall length, which really means bullet seating depth, that touches the lands (coincides with land diameter) then subtract that from what you then measure when the bullet is seated deeply enough to fit into a magazine box, that right there is the amount of jump.

Hornady LNL gage
There are other ways to find it, but the Hornady LNL Overall Length Gage makes it easy. I’d be lost without this tool. Use it to determine the current distance to engage the lands for any bullet you’ll use (it works also as a way to monitor throat erosion). Get one HERE

Dealing with an AR15, or any other magazine-fed rifle, assuming we are wanting the rounds to feed from the magazine, is that there’s a finite cartridge overall length that will fit into the magazine. So. We’re almost always going to be dealing with some amount of jump, unless one or two things can be manipulated to reduce or eliminate it.

AR15 loaded magazine
A box magazine sets the effective limit on overall cartridge length. Getting a bullet to sit close to the lands when the round is chambered requires either some trickery in chambering specs or, mostly, bullet selection. However, with selection there is also limitation. For safety’s sake, no factory loaded round is going to approach lands-on seating structure. When a bullet touches the lands at rest, pressures will, not can, spike. All good, if it’s accounted for. This sort of “fine-tuning” is strictly a (careful and knowledgeable) handloader’s realm.

The one is that the influence of rifle chamber specs with respect to either more or less jump is pretty much exclusively in the leade or throat. That’s the space that defines the transition from end of the chamber case neck area to entry into the lands. The closer the lands are to the chamber neck area the shorter the jump will be with any bullet. That is the leading difference between a SAAMI-spec .223 Remington chamber and a 5.56 NATO chamber. The NATO has a much longer throat. I’ve written on that one a few times…

A shorter throat has goods and bads. The main good is that, indeed, any and all bullets are going to be closer to the lands in a round loaded to magazine-length.

But the “two” in the things that influence jump is bullet selection. It is possible to find a combination that will easily have the bullet sitting right on or very near the lands at the get-go. That’s going to be a short, and light, tangent ogive bullet within a SAAMI-spec .223 Remington chamber, or (and this is what I have done) a barrel chamber finished using a throating reamer to get even closer. In general: the nearer the first point of major bullet diameter (remember, that’s the land diameter) is to the bullet tip, the shorter the jump will be, and that’s because this point is “higher.”

Hornady 52gr HPBT
Looking through a good factory loading manual down amongst the “lighter bullet” selections, take a notice of the overall round length used in the test ammo. Magazine box maximum for an AR15 is 2.25 inches (it’s actually 2.26 at a maximum, but don’t cut it too close). If you see a length less than that, then there’s a bullet that can be seated on or near the lands at magazine length. Simple.
Here’s a great example that I can tell you absolutely will engage the lands in an AR15 loaded to magazine length. As a matter of fact it will be over 0.020 into the lands at magazine length, so certainly must be loaded to an overall length well less than that… It also shoots little groups. Check it out HERE

Throat erosion is going to lengthen the throat. Can’t stop that. The cartridge structure that was jumping, say, 0.005 on a new barrel is jumping more than that after literally every round fired through it. After some hundreds of rounds it’s jumping a few multiples of 0.005. (How much or how many is not possible to forecast because way too many factors influence the amount and rate of throat erosion. Just have to keep checking with the gage I suggest you purchase.) This is the reason I specify a custom dimension to get reduced jump: with the right hands using a throating reamer it’s easily possible to maintain land contact at magazine length seating even after a lot of rounds have gone through. Bullets will begin being seated more deeply and then get nudged out as the throat erodes.

So, where the conversation ended was this: If (and only if) someone is willing to take the time and make the effort to carefully establish and then control a reduced or eliminated amount of magazine-loaded jump then, yes, it’s a fine idea! It’s also an idea that likely will result in the best accuracy. I’ve done it in one of my AR15 match rifles, and it’s the best shooting I’ve ever owned. The hitch is that the rifle becomes what I call a “one-trick pony.” It’s not always going to accept bullets and loaded round architectures that stray from the carefully calculated dimensions originally set down. It’s also not likely going to perform safely with every factory-loaded round out there, and you can forget (totally forget) ever firing a NATO-spec round.

There’s a whopping lot more to this whole topic, and we’ll look at the other end of the spectrum next time.

The reason that reduced amounts of bullet jump increase accuracy, in a perhaps overly simple but entirely correct way to understand it, is because there’s simply less potential for disruptive entry into and lands and then through the bore. There’s less misalignment opportunity, less jacket integrity disruption opportunity. There is a lot more that can be discussed in finer points, of course…

The preceding was adapted from Glen’s newest book, Top-Grade Ammo, available here at Midsouth. For more information on this book, and others, plus articles and information for download, visit ZedikerPublishing.com

Shooting Skills: AR15 Trigger Choice, Continued…

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Improving an AR15 trigger ranges from total redesigns to minor changes, and here are a few not to overlook.


Glen Zediker


Last time I used all the space I had talking about the two essential AR15 aftermarket styles, single-stage and two-stage. There was more to say, and here that goes:

Modular triggers
Most two-stage and single-stage triggers work off the existing AR15 trigger architecture, but there are those that don’t. Some are self-contained and self-defined. These “modular” triggers are all way on better than stock, to be sure. What they are, are complete housings that contain the hammer and trigger captive within the housing, installed, tuned, and adjusted as a unit (some are user-adjustable, some are not). They “drop in” and the housing is then secured by the original pins. The pins, however, don’t function within the trigger unit itself.

Timney
This is a Timney modular-style AR15 trigger. Take out the old trigger, drop this one in the lower, secure the stock pins through the holes in the Timney housing (and make an adjustment to secure the housing against the lower receiver floor). Done. All the modular-types I’ve tried are better than stock, indeed. I can’t warrant durability though, because a few out there look a tad amount spindly. This one has been reliable so far.

A modular trigger is about the easiest way to a better trigger. The question with the modulars is how well they hold up, how reliable they will be. There’s a difference in the natures, and outcomes, of stress-in-use comparing target shooting and varminting to the pounding a carbine might get in a 1000-round range session. I have not put a huge number of rounds through any of the modular units and, therefore, have no notebook references. I do, however, know a good many others who have and whose opinions I value. Consensus is that not all are 100-percent.

Pins
Many aftermarket triggers come with a set of proprietary pins, and if one does, use them. If not, a better pin set can make a difference in trigger performance.

KNS AR15 trigger pins
Here’s a standard-form pin set from KNS. They’re correctly and consistently sized and dead straight. Trigger pins and hammer pins are the same, but they don’t function in the same. Each pin is installed from the right side of the receiver, un-grooved end first, and pushed through to the left side of the receiver. The grooves function to engage the trigger return and hammer springs, preventing the pins from out and out coming out of the rifle. Install from the right side of the lower receiver, pushing it through to the left side, ungrooved end goes first. Lube the pins!

Look at how the system operates and it’s clear that pin straightness and circumference influence trigger break and function. The pins in the standard system are also free to rotate. If the pin is a little undersized or a little bent, or both, that means engagement won’t be consistently the same each time.

And sometimes it’s not all the fault of the pins. The receiver holes also have to be what they should be. I’ve had fit mismatches from time to time, and the way to fix it is usually in the pins, because they are usually a tad amount too small. However! It’s not always a straight-up fix to purchase “oversized” pins.

One (strong) caution if you opt for “oversized” pins: make daggone sure prior to installation that the trigger parts are fully free to move as they should on the pins. The hammer, especially, should have zero drag. Sometimes a little very careful polishing on the center point area of the pin is necessary to attain a “perfect” match.

Oversized AR15 trigger pin
Here’s an oversized pin. Check diameters with a micrometer and compare them to blueprints. Standard should be 0.1540 inches (+/- 0.0005). Oversized usually adds 0.0010. Also! Check the receiver holes. Easiest to do with a #23 machinist’s drill bit (use the butt end of it); that’s a 0.154 size (get a 0.155 also, if you can find one). Make the right match! Don’t pound an oversized pin into a smaller-size receiver hole! If you do then you’ll get into a cycle… For conflicting circumstances, KNS offers a well-oversized pin packaged with a reamer to suit. Best proceed with care, though.

To preclude pin rotation, a “locking” pin set is the trick. Even oversized pins can move. There are a few different takes on lockers, and I put a set on all my race guns.

Better pins can also make a positive difference in modular trigger installation.

KNS locking AR15 pins
Here’s a set of KNS locking pins. There are different styles, and all function to fix the hammer and trigger pins against any movement, providing an unchanging base for a match-quality trigger.

Springs
Another simple trick I do, when I can, is install a pair of chrome-silicon trigger return and hammer springs. This material is radically superior to the standard music wire used otherwise. It rebounds faster at a lighter “weight” than a music-wire-based spring. That means easier operation with no sacrifice in tension. Chrome-silicon also lasts the life of a rifle. All music wire springs will break down and lose power, so simple replacement of the hammer spring every 2500 rounds or so can be a maintenance routine item to maintain peak performance. Trigger return springs, no so much. They’re not under much stress.

A chrome-silicon replacement set will reduce trigger pull effort a tad in a stock setup, but unfortunately won’t do a thing to improve its movement quality.

An extra-power hammer spring is a commonly-used addition to a competition gun, and the reason is pretty much to reduce hammer fall time. It works. However, be warned that an extra-heavy spring can wear the receiver holes; after some time, the holes can get a little oblong and, along with it, larger. If you want to run a heavy spring, get a very well matched fit prior to installation of the spring. This stays off hole wear because there’s just no room for movement.

CS AR15 trigger and hammer springs
A chrome-silicon spring pair will improve trigger pull some, but mostly these springs last for a good long while. They just don’t change over 100,000+ cycles. Chrome-silicon has better rebound behavior so the hammer hits a little quicker. I use them in any trigger where they’ll fit. These are manufactured by David Tubb, Superior Shooting Systems.

Lube the fool out of the trigger! Simple as it may seem, keeping the works slicked up goes a long way toward making a trigger feel better and last longer. By “last longer” I mean retain consistent feel and weight. This is especially important in a two-stage. It can’t be over-lubricated. I use light grease with boron-nitride for the engagement surfaces and hammer face (bolt carrier slides across this) and oil for the rest of it.

The only exception is for those who are out in the field in sandy and dusty conditions, or in extreme cold, and then I’d suggest one of the “dry” lubes. But some lube always!

AR10
If you have one of these, make double-dang certain your new trigger is performing correctly. The AR-10/SR-25 types are beastly in cycling. When that honking bolt carrier slams back home after chambering a round, the inertia residing therein can trip a lot of the aftermarket triggers. It’s a shock. What happens is the disconnector, well, disconnects and loses its previously captive hammer. Especially some of the modular units just won’t function safely on a big-chassis rifle.

The preceding was a specially-adapted excerpt from the book The Competitive AR15: ultimate technical guide by Glen Zediker and Zediker Publishing available from Midsouth Shooters Supply.

Shooting Skills: AR15 Trigger Choice

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A better AR15 trigger means a different AR15 trigger. Which essential type is right for you?


Glen Zediker


Good triggering mechanics aren’t wasted on a bad trigger, but a good trigger can quickly increase triggering skill. And, no kidding, it’s way on easier to control a shot break with a trigger that’s consistent and at the least not “heavy.”

So you have an AR15… We don’t really much talk about stock AR15 triggers. They’re bad. They’re safe and reliable, but it’s such a “mousetrap” design that it’s really not likely to make improvement using conventional approaches, namely files and stones. The metal is heat-treated and the hardness is shallow. Any intrusion beneath the surface of the sear (the nose-end of the trigger bar assembly) or the hammer hook reveals soft metal, too soft to maintain a geometry change.

One of the first to address improving the AR15 trigger system, the JP Ent. solution is essentially standard-form architecture with precision revisions. Notice the adjustment screws, lightened hammer, and proprietary springs. It’s a clean, light single-stage. It’s been a favorite of some of the speed demons in practical rifle and 3-Gun events.
One of the first to address improving the AR15 trigger system, the JP Ent. solution is essentially standard-form architecture with precision revisions. Notice the adjustment screws, lightened hammer, and proprietary springs. It’s a clean, light single-stage. It’s been a favorite of some of the speed demons in practical rifle and 3-Gun events.

So. We rely on aftermarket trigger systems. There are a good many. Problem is that not a many are good. This article will address trigger systems from a more “general” or overview approach. Yes. I have favorites. Yes, also, there are a few I don’t like. I’m more liable to name names in my books than I am here over the interweb in front of God and all the neighbors, and that’s because my preferences are largely subjective.

The aftermarket began addressing AR trigger issues a good long while ago, and the first idea was to produce essentially the same hammer and trigger pieces, but with improved precision and better geometry, mostly improved precision, in the mating surfaces, plus some mechanism adjustment means. The next steps were total redesigns, including adaptations from other systems. I’ll focus this rest on one of those designs.

Now I hope also to answer a question that I get time after time after time. It would be hard to have shopped AR15 replacement triggers and not come across “two-stage” triggers. So, the question is, “What’s a two-stage trigger?”

Here’s the original AR15 two-stage, and how it works. Developed by Charlie Milazzo and John Krieger, the MKII changed life for competitive AR15 shooters. There is still no better trigger for these rifles, in my opinion. Just a little difficult to find. This is a true two-stage (primary and secondary sear). There is zero question in my mind that two-stage triggers are safer, and even less question that they’re easier to develop triggering skills with. You’ll see.
Here’s the original AR15 two-stage, and how it works. Developed by Charlie Milazzo and John Krieger, the MKII changed life for competitive AR15 shooters. There is still no better trigger for these rifles, in my opinion. Just a little difficult to find. This is a true two-stage (primary and secondary sear). There is zero question in my mind that two-stage triggers are safer, and even less question that they’re easier to develop triggering skills with. You’ll see.

What it is, is, well, it is what it does: there are two separate and distinct stages or steps to the trigger pull. In a true two-stage, the first stage is free-run, of varying distance and resistance, taking up the secondary sear, and then there’s a stop, which is the primary sear engagement. Then any more pressure drops the hammer. So it pulls back, stops, and from that point, the shooter decides when to loose it. Or not. Shooter can let the trigger back forward, regroup, and go at it again. Being able to get on and off the trigger, and feeling it stop against the second stage, makes for a more competent, confident shooter. We know with certainty when the shot is going to fire. We’re in full control of it. We’re already holding some tension on the trigger. Makes the next bit easy. A two-stage doesn’t have the “delicate” feel of a single-stage.

Here’s another take on the two-stage from Arnold Jewell. It’s different. Very good trigger in action, but a little sluggish in its hammer fall. It’s one of the best feeling triggers I’ve used, and it’s nicely and easily adjustable. If you get a two-stage, make double-dang-sure you “stage it.” Feel the stop and learn to exploit it. It can transform your skill level.
Here’s another take on the two-stage from Arnold Jewell. It’s different. Very good trigger in action, but a little sluggish in its hammer fall. It’s one of the best feeling triggers I’ve used, and it’s nicely and easily adjustable. If you get a two-stage, make double-dang-sure you “stage it.” Feel the stop and learn to exploit it. It can transform your skill level.

This style is the preeminent design used in serious purpose-built competition rifles, and this trigger type has also been integrated into previous U.S. Armed Forces rifles, namely the M1 and M14.

Safety is the primary reason a two-stage was incorporated into service-rifle designs. As said, the two-stage gives the operator a clear signal. Unintentional shot release is far less likely.

There are a number of two-stage triggers available for AR15s. They vary widely in cost, and also in quality. Any and all, though, are a radical improvement over stock. For those looking primarily to fire focused, accurate shots, I very strongly recommend a two-stage. They are the bomb for “common” shooting circumstances.

But. They’re not for everyone, not for every application. Here’s what’s bad about two-stage triggers. First, foremost, and most noticeable, is the relatively huge distance-to-reset compared to a single-stage. Trigger “reset” is when the disconnector (which has captured the hammer as the carrier cycles) hands off the hammer to the sear. The hammer can’t fall again until the trigger resets, so the trigger can be pulled again. The trigger resets when it’s let back far enough forward to activate the sear. There is some amount of reset distance in any semi-auto trigger, and the AR15 already has a significant amount. The amount of movement from being pulled fully to the rear and let back forward until reset is what I’m talking about here.

Rapidly successive shots are a challenge with a two-stage. 3-Gun-type shooters, or any who are in wants or needs to fire shots in very rapid succession, are more effective with a good single-stage. All that swing in the trigger, back and forth, back and forth, is not conducive to best performance in hosedown-mode. It’s harder to ride the trigger at higher and higher speed when the trigger travels so far.

Next time I’ll talk more specifically about options and also the “modular” or “drop-in” AR15 triggers, plus a few tips and tricks to make any AR15 trigger better.

Okay. I’ll tell you. All of my competition rifles carry one of these, self-tuned. It’s a Geissele Automatics two-stage. There are several different versions from Geissele. This is the “match” variety. It’s very tunable, if you know what you’re doing, and the hammer hits quickly. Bonus.
Okay. I’ll tell you. All of my competition rifles carry one of these, self-tuned. It’s a Geissele Automatics two-stage. There are several different versions from Geissele. This is the “match” variety. It’s very tunable, if you know what you’re doing, and the hammer hits quickly. Bonus.

The preceding was a specially adapted excerpt from The Competitive AR15: ultimate technical guide. Available from Midsouth Shooters Supply, for more information visit Zediker Publishing.

5 Steps to “Pressure-Proofing” Handloads

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Here’s a few ideas on how to proceed in load testing to find the safe maximum velocity, and keep it safe…

We’ve chosen the sometimes twisting path to becoming handloaders because we want to improve on-target results. The difference between a handloader and a reloader? My wise-crack answer, which is honest, is that handloaders start off with new brass… We’re not about to shoot factory ammo.

Part of the process of developing the load we’re seeking is learning how to safely set a cap on its pressure. Most of us don’t have pressure-testing equipment, so we rely on measurements and observation to know when we’re at the limit. The goal often, all other things being the same, is to find the highest velocity we can get. Less drift and drop, shorter time of flight, all good. However! Knowing that the maximum tested velocity is also going to be safe over the long haul is a much narrower line to walk.

There’s not room here to cover every pressure check, all the symptoms that can point out over-pressure ammo, but I’ll share my two leading indicators: primer pockets and velocities.

  1. Always start load development with new brass! There are a few reasons, but the leading one related to this material is that the primer pockets will be at their smallest. So. Fire the cases, size the cases, and seat new primers. It takes a little experience, which means a few times through this process, but my leading indicator of pressure is how easily the primers seat. They’ll go in easier than on the first use, but if there is much less to very little resistance felt the second time around, that load is over-pressure. Period. The case head has expanded (I put a max of 0.0005 on expansion, when it’s measured with a micrometer). The more you use the same cases and repeat this process, the sooner you’ll get a handle on the feel to know when the primer pocket has overly expanded.
seating primer to check pressure
My primary gauge for pressure is primer seating — how easily a new primer seats into a once-fired case. This is an indication of case head expansion. It won’t be as tight as new, but it should still be snug. A low-leverage tool, like this Forster Co-Ax, increases the feel and feedback of this operation.
  1. Jump back, don’t step back. If you encounter a pressure symptom, come off a “whole” half-grain. Not a tenth or two. And if you see it again, come off another half-grain. Folks, if anyone thinks the difference between over-pressure and safe-pressure is 0.10-grain, that same little bit exists in the difference in 20-degrees ambient temperature with many propellants. Don’t cut it that close. Keep the long-haul in mind.
  1. Select a temperature-insensitive propellant (related to the above). There will be one out there you’ll like. I use a single-base extruded (stick) propellant when loading for the season. The propellants I choose are coated to help reduce temperature-induced changes. That season is going to span a 50+-degree range, and I don’t want August (or October) to force me back to the loading room… Temperature sensitivity works “both” ways, by the way… Hot or cold can induce pressure increases.
  1. Read the speed on each and every round tested. Beforehand, I have to assume you’ve gotten an idea in mind of what you’re looking to get for a muzzle velocity. If not, do that… A journey of this nature has to have a destination. If not you won’t know when you get there. If you are reading velocities more than 40-50 feet per second over a published maximum, that’s a flag. That 40-50 fps is usually about a half-grain of most propellants in most small- to medium-capacity cases. Certainly, there are all manner of reasons some combinations can vary, but, despite what your mother might have told you, you are really not THAT special…
  1. Don’t assume anything. If you have one round out of many that “suddenly” exhibits pressure symptoms, don’t guess that it’s just a fluke. It’s not a fluke. You finally saw it. Overwhelming chances are that the load is over-pressure and has been over pressure, and the question is how much for how long? Back it off. (The way you know it might have been a fluke, and that happens, is again based on how close to a velocity ceiling it is: if it’s a real mid-range velocity load, it might have been a fluke.)
primer indicators for over-pressure ammo
Some over-pressure indications are pretty clear. Left to right: new, nice and safe (notice there’s still a radius on the primer edge), cratered and flat, yikes! It’s another article, but not all piercings are caused solely by high-pressure ammo; an overly large firing pin hole size in an AR15 bolt contributes.

One last about primer appearances. Usually the first thing a handloader will do after firing a round is look at the primer. I do. No doubt, if the primer is flattened, cratered, pitted, or pierced that’s a honking red flag, and the immediate response is, you guessed it, come off a “whole” half-grain. However. Small rifle primers (especially some primers in some cartridges) do not exhibit the common over-pressure appearances. They can look just fine and shiny until they blow slap out. If you ever see anything that looks like a pressure symptom, back it off; however, don’t assume a load can’t be running hot if the primers don’t show it.

over pressure ammo, primer appearance
Here’s what I mean about primer surface indications not always revealing high pressure. The middle one is an incredibly over-pressure load fired through one of my AR15 race-guns with an extra-heavy bolt carrier. Primer looks just fine. Right hand case is what happened without the extra weight. Neither case would hold a primer after this one firing.

Back to the start: primer seating and velocity are the leading indicators.


The preceding contains specially-adapted excerpts from the new book “Top-Grade Ammo” by Glen Zediker and Zediker Publishing. See it by visiting ZedikerPublishing.com.