Tag Archives: reloading safety

RELOADERS CORNER: Pressure Signs

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We usually want the most velocity we can SAFELY get, and here’s all about how to stay safe. Keep reading!

Glen Zediker

I’ve been on the topic of load development — “working up” a load — for the past couple of editions, and, based on the excellent feedback from you all, here’s more. As always, there’s only so much I can write before I have to cut myself off.

I’ve said that velocity is the initial leading indicator of pressure. Velocity, in itself, however, is not a definitive indicator of pressure. I’d like to clarify… The first point is that I am a big believer in establishing a goal for load development, and, for me (and likely most others) that is a velocity. Accuracy is a given! I will never consider a combination that’s not shooting little knots downrange, but accuracy and velocity are not mutually exclusive. I also would never consider a combination that produced very small groups at an unacceptably low velocity, and that’s because I’m shooting (always) beyond 200 yards. The super-accurate low-velocity load gets its bullet shifted that much more in a variable wind, so it’s way on less likely to maintain those small groups.

I want to hit the velocity ballpark I have in mind and that’s why chronograph readings as I’m incrementally increasing the propellant charge are my leading indicator to how close I’m getting. I am also, always, looking for pressure signs on the spent cases — each and every one ejected.

So about those pressure signs…

Primer condition gets first attention.

primer pressure signs
Middle is what I want to see: pretty much a new primer with a nice round dimple in the center. Right, well. Massive pressure! But notice that the primer still shows a radius on the edges and is only a little rougher in appearance, well, aside from the crack…

A primer should have a smoothly dimpled firing pin indention, a shiny appearance, and a visible radius on its edge. If any of those are missing or compromised to varying degrees, there’s your sign… A dull and flattened primer has been abused, as well as one with a pitted or cratered appearance. Clearly, a crack or leak (indicated by black fouling) is way over the limit. After experience, backed up by gauged measurements, you’re liable to find that judging what’s “normal” and “safe” from one rifle can be different from another. I have had individual guns that flattened primers at any point near a safe-maximum charge. And, I’ve had them that just lied. Unfortunately, small-rifle primers don’t show always show pressure signs as reliably as large-rifle primers (structural differences). I’ve had experiences where the primers are all nice and shiny like and then blow out with the next increment. Shame on me for taking it there, and, speaking of: don’t get greedy! That’s one reason a velocity goal is important. Despite what your kindergarten teacher told you, you’re not that special… If you’re reading another 50+ feet per second more than what consensus says you should, better bet you’re over-pressure. “We” went through a lot of that when coated bullets got popular: those changed all the rules for “maximums.”

flattened primer
Here’s flat. My experience has been that large-rifle primers tend to display this indication more so than small. What’s happened is that the primer has flowed quite forcibly to fit the confines of its pocket and the bolt face. It’s also normal for some rifles, but that just means you have to know: pay attention and back off if you see a flattened primer.

The best pressure indicators show at the loading bench.

primer seating
My best “gage” for pressure is seating a primer in a fired and resized case. It’s a feel, gained through comparative experience, but too easy means there was too much pressure.

The reason I suggest (strongly) doing load work-up with new cases is because you then have a baseline. Measure the case head diameter (on the case, not the rim or groove) on the new case and compare it to the fired case. Up to 0.0005 (that’s ten-thousandths) is really high but some say acceptable (not me), and 0.0002-0.0003 is what I’d prefer. Plus, since a new case is at its smallest, meaning it will have a little less capacity than a fired case, you’re getting some assurance that the pressure will likely be a little lower from the same load in subsequent reuses of that case.

All dimensions are at their minimum in a new case. Primer pocket expansion is related to case head expansion. I get (what’s proven to be) a very accurate indication of pressure based on the resistance to seating a primer in that resized case. You have to use a priming tool that gives adequate feedback (meaning low leverage) but if the primer just slips right back in, that load was over-pressure. In a more extreme circumstance, the primer won’t stay seated. Yes. I have seen that. Shame on me, again.

Finally, a new case easily points out the difference between a “pressure ring” and a “sizing line” that can show just above the case head along the case body. A bright ring there indicates excessive stretching (a sizing line comes from the die reducing that area, and is perfectly normal). That “pressure ring” sign is also likely an “improper headspace” sign, but that’s another article.

pressure ring
Here’s a “pressure ring.” This poor old fellah used to be a brand-new Lake City Match case. I suspect there was some issue with this rifle’s headspace, but if you see this bright stretch mark, red flag it! It means the case is going to crack right there next use (called an “insipient head separation”).

Pierced Primers
This is a common malady on AR-platform guns, and especially on the big-chassis versions (SR-25, AR-10, and similar). Pressure both isn’t and is the culprit and the solution. Lemmeesplain: What causes the pierce is a firing pin hole that is too large. It is not the fit of the firing pin tip to the hole! An engineer can explain it, but it has to do with surface area covered by the firing pin hole, and then along with it the surface area of the primer. Simply: the firing pin hole turns into a cookie cutter. A primer pierce creates all manner of ills, including wrecked firing pins, gas flow through the charging handle area (where your face is), and abrasive debris scattered throughout the lower interior, including the trigger parts.

firing pin hole size
Blueprints call for a 0.058-inch diameter firing pin hole on an AR15 bolt. If the hole is too large then primer structural failures (pierces) will, not can, rear up. Too big is anything more than 0.062 inches, and I’ve seen plenty bigger than that. I use machinist’s drill bits to quick-check bolts: 1/16 (0.0625) and #53 (0.0595). If the first fits the hole, find another bolt. If the #53 won’t go, use that bolt with confidence.
pierced primer
Notice that this primer doesn’t really show excessive pressure signs. Just has a hole in it…

Excessive pressure gets blamed for a pierce but what’s really going on there is that it’s not certain that amount of pressure would be judged as “excessive.” It’s just gotten high enough to bring on this result. So, yes, lightening the load will stop the piercing, but, in my experience and that of many others, the pierces can start happening before reaching what most might agree on is a max load. I say that because “we” are all shooting about the same bullet/primer/case/propellant combinations in NRA High Power Rifle (with respect to Service Rifle division AR15s, for instance). Seeing pierced primers before hitting the proximity of competitive velocities points to “something else,” and that is the firing pin hole.

In a truly over-pressure load, the primer can crack or blow slap out, but it won’t pierce.

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: Priming, Part 2

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Last time the tooling and process of seating a primer got detailed, and now more details about The Thing Itself. Read all about it…

primer close up

Glen Zediker

A primer consists of a brass (usually) cup filled with impact-detonated explosive compound, lead styphate specifically. Right. Primers explode. The compound starts as liquid, not that that matters, and while it’s still wet, a triangular metal piece called an “anvil” is positioned in the opening. When it’s hit by the firing pin, the center of the cup collapses, squeezing the explosive compound between the interior of the cup and the anvil. That ignites the compound and shoots a flame through the flash hole. That ignites the propellant.

There are two primer sizes, and then type variations. The two sizes are “small” and “large.” For example, .223 Rem. uses small, .308 Win. uses large. Rifle primers and pistol primers are not the same, even though they have diameters in common. Rifle primers have a tougher cup, and, usually, provide a hotter flash. Do not substitute pistol primers for rifle primers! Some pistol shooters using very high-pressure loads substitute rifle primers, but also often need to increase striker impact power.

Variations: There are small variations in primer dimensions, heights and diameters, and also variations exist in new-case primer pocket dimensions, among various brands, and, of course, lot-to-lot variations can and do exist within any one brand. Usually, these variations are not influential to suitability. Usually. However! On occasion, small diameter variations can affect how well different primers will feed through various make priming apparatus. This can and has become a hitch in some progressive loading machines. Cup height variations can lead to seating depth (primer height) issues.

Remington 7-1/2 primers
I have my “go-to” primer, as do most, but I’ve found best results in certain circumstances with another brand. I will not vary primers, though, in my tournament ammo for any one day: as with propellants and bullets, each leaves a different residue in the bore, and that will, not can, influence zero making the switch. In other words, I won’t use CCI for short-line loads, and Remington for 600-yard ammo, not on the same day.

There are also “magnum” primers. These have a hotter spark. They are engineered to deliver a stouter kick-off to larger, more dense columns of slower-burning propellant. They also work well with spherical-type propellants (less air space between the granules). There are also “match” primers. These ostensibly are more consistent quality. Not all manufacturers offer these options. If they do, unless you have a scheme or more carefully-considered reason, just go with what fits your application. There’s no need for match primers in blasting ammo. There are, no doubt (and no doubt significant) differences among varying brand primers with respect to “output.” As mentioned earlier on, there are also pretty well-known tendencies that are either more or less preferable among varying primer brands.

The primer is, in my experience, the greatest variable that can change the performance of a load combination, which is mostly to say “pressure.” Never (never ever) switch primer brands without backing off the propellant charge and proving to yourself how far to take it back up, or to even back it off more. Don’t deny this one.

I back off one full grain of propellant to try a different primer brand.

Finding the best-performing primer for any particular combination of cartridge, bullet, and propellant isn’t just always as easy as putting a “match” primer in there. I have my preference, and it’s what I try first, but, to be certain, sometimes best accuracy and consistency (related) come with another. Again, it’s a combination of propellant fill volume, burning rate, propellant type (single-base, double-base, extruded, or spherical), and column “packing” density that favors either a “hotter” or “cooler” flash.

Priming cup composition also factors mightily in my final choice, and that’s a big factor in some semi-autos. More next time.

primer tray
Here’s handy. A primer “flip” tray puts all the primers in the sams orientation and orients them for easy loading into a primer magazine feed tube for use in many automated systems. See what’s available at Midsouth HERE

SAFETY
Do be extra careful handling primers! No kidding. It’s the most explosive element in a cartridge, and it’s intended to be detonated from impact, so… Wearing safety glasses at the loading bench might seem nerdy, but it’s wise. Likewise, and this has happened way on more than once, but, fortunately, never yet to me, is a mass detonation of primers contained in a feeding device, such as a primer feeding magazine tube. Such circumstance is grave indeed. Progressive loading machines, as well as many bench-mounted appliances, use a tube magazine that contains the primers. This tube must be filled, like any magazine. Make sure you know when full is full, and don’t try to poke in one more. This is usually when “it” happens. Remember, primers are detonated via pressure. Said before, but important enough to say again now: Never (ever) attempt to more deeply seat a primer on a loaded round. And keep the priming cup (the tool part that holds the primer for seating) clear of all debris. I’ve heard tell of brass shavings, leftover tumbling media, and the like, getting between the primer and the tool cup, and forming its own little firing pin.

See what’s available 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: REALLY Understanding Case Neck Sizing

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Determining and setting the correct case neck diameter is a critical, crucial step in the handloading process: Here’s all you need to know!

sizing die bushing

Glen Zediker

Here’s another I get (too many) questions about, and when I say “too many” that’s not at all a complaint, just a concern… This next hopefully will eliminate any and all confusions about this important step, and decision, in the reloading process.

Basics: A cartridge case neck expands in firing to release the bullet. If the load delivers adequate pressure, it can expand to the full diameter allowed by that portion of the rifle chamber. That diameter depends on the reamer used. After expansion and contraction, the case neck will, no doubt, be a bigger diameter than what it was before being fired.

Back to it: To get a handle on this important dimension, the first step is tools. As always. A caliper that reads to 0.001 inches will suffice.

You need to find three outside diameter numbers: fired case neck diameter, sized case neck diameter, loaded case neck diameter. If you know the loaded case neck diameter then it’s likewise easy to find out the case wall thickness, or at least an average on it if the necks aren’t perfectly uniform (and they won’t likely be unless they’ve been full-on outside case neck turned).

Case neck sizing diagram
“All the math” works in either direction. Here’s how.

A fired case neck has to be sized back down to a dimension that will retain a bullet from unwanted movement (slippage) in the reloaded round. Case neck “tension” isn’t really an accurate term, in my mind, so I prefer to talk about “constriction.” The reason is that making a case neck diameter smaller and smaller does not, after a point, add any additional grip to the bullet. Once it’s gotten beyond maybe 0.005 inches, it’s just increasing the resistance to bullet seating not increasing the amount of tension or retention of the case neck against the bullet. The bullet is resizing the case neck, and probably getting its jacket damaged in the process. If more grip is needed, that’s where crimping comes in…and that’s (literally) another story.

IMPORTANT
Always, always, account for the “spring-back.” That is in the nature of the alloy used to make cases. If brass is sized to a smaller diameter it will spring back plus 0.001 inches bigger than the tool used; if it’s expanded to a bigger diameter, it will spring back (contract) to 0.001 inches smaller than the tool used. This is always true! The exception is that as brass hardens with age, it can spring back a little more.

How much constriction should there be? For a semi-auto, 0.003 is adequate; I recommend 0.004. For a bolt-action, I use and recommend 0.002, and 0.001 usually is adequate unless the rifle is a hard-kicker. See, the main (main) influence of more resistance in bullet seating is to, as mentioned, set up enough gripping tension to prevent unwanted bullet movement. Unwanted movement can come from two main sources: contact and inertia. Contact is if and when the bullet tip meets any resistance in feeding, and gets pushed back. Intertia comes from the operation and cycling of the firearm. If there’s enough force generated via recoil, the bullets in rounds remaining in a magazine can move from flowing forces. However! That also works literally in the other way: in a semi-auto the inertial force transmitted through a round being chambered can set the bullet out: the case stops but the bullet keeps moving. I’ve seen (measured) that happen with AR15s and (even more) AR-10/SR-25s especially when loading the first round in. Put in a loaded magazine, trip the bolt stop, and, wham, all that mass moves forward and slams to a stop. Retract the bolt and out comes a case with no bullet… Or, more usually, out comes a case with the bullet seated out farther (longer overall length). Never, ever, set a constriction level on the lighter side for either of these guns.

Most seem to hold a belief that the lower the case neck constriction the better the accuracy. Can’t prove that by me or mine. If there’s too much constriction, as mentioned, the bullet jacket can be damaged and possibly the bullet slightly resized (depending on its material constitution) and those could cause accuracy hiccups. If it’s a semi-auto and constriction is inadequate, the likewise aforementioned bullet movement forward, which is very unlikely to be consistent, can create accuracy issues, no doubt. My own load tests have shown me that velocities get more consistent at 0.003-0.004 as compared to 0.001-0.002.

Benchrest competitors use virtually zero constriction, but as with each and every thing “they” do, it works only because it’s only possible via the extremely precise machining work done both in rifle chambering and case preparation. It is not, decidedly not, something anyone else can or should attempt even in an off-the-shelf single-shot. As always: I focus here, and in my books, on “the rest of us” when it comes to reloading tool setup and tactics. Folks who have normal rifles and use them in normal ways. And folks who don’t want to have problems.

So, find out what you have right now by determining the three influential diameters talked about at the start of this article. Most factory standard full-length sizing die sets will produce between 0.002 and 0.003 constriction. Getting more is easy: chuck up the expander/decapper stem in an electric drill (I use oiled emery cloth wrapped around a stone), and carefully reduce the expander body diameter by the needed amount, or contact the manufacturer to see about getting an undersized part. I’ve done that.

polish expander
It’s easy to increase case neck constriction if you’re running a conventional sizing die setup that incorporates an expander or sizing button. Just make the button diameter smaller; then it won’t open up the outside-sized case neck as much as it is withdrawn from the die and over the expander.

If you want less constriction than you’re currently getting, about the only way to do that one is hit up a local machinist and get the neck area in the die opened by the desired amount (considering always the 0.001 spring-back). Or get a bushing-style die…

Redding S Die
It’s not perfectly necessary to use an inside case neck expanding tool if you’re using a bushing-style die. I think it’s wise for a multitude of reasons I’ve gone on about in the past, and may should again, but if the math is carefully done, and the cases are all same lot, outside neck reduction will result in consistent inside case neck diameter sizing. Example: Case neck wall thickness is 0.012, outside sized case neck diameter is 0.246 (from using, remember, a 0.245 bushing), then the inside case neck diameter will be 0.222, and that will be a 0.002 amount of bullet constriction (0.224 caliber bullet).

The bushing-style design has removable bushings available in specific diameters. Pick the one you want to suit the brass you use. If you run an inside case neck expanding appliance along with a bushing die, usually a sizing-die-mounted “expander ball” or sizing button, make sure you’re getting at least 0.002 expansion from that device. Example: the (outside) sized case neck diameter should be sufficiently reduced to provide an inside sized case neck diameter at least 0.002 smaller than the diameter of the inside sizing appliance. That’s done as a matter of consistency and correctness that will account for small differences in case neck wall thicknesses. And when you change brass lots and certainly brands, measure again and do the math again! Thicker or thinner case neck walls make a big difference in the size bushing needed.

Check out a few ideas at Midsouth HERE

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