Category Archives: Reloading Corner

Five Steps for Preparing New Brass

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These are brand-new high-dollar Lapua cases, which the author points out are a tad amount deformed about the case mouths. Most new cases will show this sort of irregularity. Just run them through your sizing die. It’s not so much establishing the neck size (although that’s wise also), but just rounding them out to accept a bullet. Also, lube new cases just like normal; even though they’re smaller than they will be after the first firing, they’re not that small.
These are brand-new high-dollar Lapua cases, which the author points out are a tad amount deformed about the case mouths. Most new cases will show this sort of irregularity. Just run them through your sizing die. It’s not so much establishing the neck size (although that’s wise also), but just rounding them out to accept a bullet. Also, lube new cases just like normal; even though they’re smaller than they will be after the first firing, they’re not that small.

For the handloader, it’s a great feeling to pop the flaps open on a new box of cases. New, shiny cases are a treat. However, new cases are not ready to load out of the box, and a look over them shows why — most will have noticeably dinged and dented case mouths. Here are a few tips on getting new brass ready to load:

Check Them All for Flash Holes

An easy flaw to watch for is a case without a flash hole. This is rare indeed, but I’ve seen one, and a few of my high-volume pistol-shooting friends have encountered more. Flash holes are almost always punched, but tooling isn’t perfect, or it breaks and goes unnoticed. I actually look at all of them just to get it off my mind.

Don’t Seat a Bullet to Size Case Necks

At the least run all the cases through a die that will size the outside and inside of the case necks. I just use my normal-duty sizing die. That way, I’ve also set case-neck dimensions to what I decided on; that means performance results consistent to my later loadings on these cases. There is not, or sure should not be, any worry about setting the case shoulder back to a shorter dimension than the new case has, if (and only if) the sizing die was adjusted in accordance with the concepts and process I outlined in the past articles.

Chamfer the Inside of the Case Mouth

After sizing, the next required step is to put a chamfer on the inside of the case mouth. The outside won’t need chamfering, unless you’ve decided to trim the cases.

I trim all my new cases, even though it’s not really necessary. For me, it’s more about squaring the case mouth than about shortening length. They’ll be plenty short enough. Just as I use the sizing die, I trim to the usual setting on my case trimmer that I have for used cases.

By the way, this is a simple way to set trim-to length on a case trimmer: Adjust the cutter head inward until it just touches the case mouth all the way around. That will be suitable from there on. Trimming, however, is purely optional.

Now the cases are ready to load. But there’s more you can do to get top results.

Do Any Other Case-Prep Steps

Any additional case prep steps are best done right now when new brass is at its softest. Especially if you want to outside-turn case necks, new brass is notably easier to work with. The exception is that I wait until after the first firing to do any primer-pocket uniforming. New primer pockets are snug.

Speaking of that first firing… This is important. “Fire-forming” is a term usually associated with describing changing a cartridge from its parent or original state into another state, which is a non-standard cartridge, when it’s first-fired in the non-standard chamber. Like making an Ackley-Improved version of a standard cartridge, or converting a .250 Savage into a 6XC. In other words, the firing itself expands and reforms the case to the shape of the new chamber. But! All cases are fire-formed to the chamber they’re fired in. That’s a lot of what I’ve been addressing in the past few articles.

Segregate Special Brass

I segregate my brass for my tournament rounds, and I do that when it’s new. Criteria and means are another article, but the reason I mention that now is because I select my “600-yard” cases, “300-yard,” and “200-yard” cases at the beginning, looking for the best, better, and good cases, respectively, for the three distances.

I need to know which are which before I make the initial loading because brass has a memory. More technically, it’s a “shape-memory effect,” a property that is shared by some other alloys also. It expands and contracts in a consistent pattern during each use.

Do not first-fire cases using a lighter (less pressure) load unless you intend to continue to use that load. Fire-forming with a lighter load and then using a nearer-to-max load in that same case will result in premature failures in that case. It doesn’t seem to matter much going the other direction, but, for instance, I would never charge up my 600-yard load in a case formed using my 200-yard load; there are significant pressure differences in those two.

And don’t forget to get dimensional checks and records on your new cases!

About the only (reasonably affordable) new brass that I’ve used that doesn’t need any pre-firing help is Nosler Competition Brass, but I still size it to ensure I’m running the same neck dimensions, and ostensibly bullet retention levels as I will on subsequent uses. There’s processed and prepped once-fired out there available through many outlets, but I still suggest sizing it.
About the only (reasonably affordable) new brass that I’ve used that doesn’t need any pre-firing help is Nosler Competition Brass, but I still size it to ensure I’m running the same neck dimensions, and ostensibly bullet retention levels as I will on subsequent uses. There’s processed and prepped once-fired out there available through many outlets, but I still suggest sizing it.

 

 

 

Case-Sizing Addition: Apples, Oranges, and Bananas

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The following is a specially-adapted excerpt from the forthcoming book, “Top-Grade Ammo,” by author Glen Zediker, owner of Zediker Publishing. Click here to order from Midsouth.

by Glen Zediker

First, I want to thank everyone who’s reading “Reloaders Corner,” and especially those who take the time to post comments and questions. That’s the fun of the web for me: it’s a closer connection to my readers and fellow shooters. Judging from a few responses to the last couple of articles on case sizing, I’d like to offer a little more detail to ensure there’s been no misunderstandings or misinterpretations.

Here’s a nice 1000-yard target from David Tubb, 11-time NRA National High Power Rifle Champion, 6-time NRA High Power Long Range Rifle Champion, two-time Wimbledon Cup winner, and current Long Range World Champion. This target was fired from prone using full-length-sized cases, with carefully constructed rounds. The rifle is a TUBB 2000 bolt-action chambered in the 6XC cartridge. Tubb sizes the case bases an additional 0.0005 smaller than SAAMI specs, and sets the case shoulders back 0.002 inches.
Here’s a nice 1000-yard target from David Tubb, 11-time NRA National High Power Rifle Champion, 6-time NRA High Power Long Range Rifle Champion, two-time Wimbledon Cup winner, and current Long Range World Champion. This target was fired from prone using full-length-sized cases, with carefully constructed rounds. The rifle is a TUBB 2000 bolt-action chambered in the 6XC cartridge. Tubb sizes the case bases an additional 0.0005 smaller than SAAMI specs, and sets the case shoulders back 0.002 inches.

I don’t have a lot of space here to cover all the smaller but often important peripherals associated with any larger topic. In the few hundred words I have available, it has to be a more specific treatment of a more specific thing, and that’s why I’ve been doing some of this material as series installments. There are a number of folks who claim neck-only sizing is necessary for best accuracy, and, in effect, that full-length sizing is a compromise, favoring function over accuracy. I want to use this space here this time to clarify a few potential confusions. And I’m not even really disagreeing with anyone.

To review, neck-only sizing is when only the case neck, all or some portion of it, is sized to adequately retain a bullet for another firing. The case body is not touched by the die interior, and the case shoulder may or may not be set back; that depends on the die design and operator preference. The idea is to better preserve the fired case dimensions; that is, make the case more closely mirror the rifle chamber’s dimensions. One advantage of neck-only sizing comes to those who expect dozens of loadings from a case. This tactic does, indeed, minimize case stretching on subsequent firings.

Mostly, do not get the impression that full-length sizing — essentially following the steps and methods I suggested in the past two articles — is short-circuiting on-target accuracy. It’s not. Not if tooling is what it should be and the operator makes the investments in money and time to gauge influential dimensions.

ejector and spring
One old accuracy trick is to reduce ejector pressure. That’s easily done in most rigs: just shorten the ejector spring, if you know what you’re doing. The author does that, or has it done, on all his rifles. The ideal amount is to have a stress-free contact of the spring against the ejector at installed height, such that the spring isn’t compressed until the ejector moves in as a round is chambered. That’s usually the minimum pressure needed to make it functional and doing its job 100%.

There are some who maintain that they only get good groups from neck-only sizing, and, moreover, that they get gatherings rather than groupings when they full-length resize, or when they use factory ammo. There can be some reasons for that, and they may have something to do with rifle-chamber dimensions.

A lot of factory-produced bolt-actions have fairly generous chambers; they are a little larger diameter and usually favor toward the longer end in headspace (but with all numbers within SAAMI tolerance). A rifle produced for across-the-counter sale needs to accept virtually any commercially available ammunition. If someone measures as many representatives of factory ammo as I have, it’s pretty clear that there are dimensional differences, significant differences. Additionally, it’s common to find some slightly oval chambers in factory guns. That has a lot to do with the freshness of the tooling when that barrel was reamed.

So, let’s construct a circumstance where we have a chamber that’s a tad amount big and a cartridge case that’s been manufactured on the smaller end of SAAMI blueprints. And this rifle has an ejector. As soon as the bolt closes, the ejector is bearing against the case, and it’s bearing well off-center.

For more clarity: rifles have extractors and ejectors. The extractor is the “claw” that rides in the case rim groove. It’s there to pull the case from the chamber. The ejector is a small, cylindrical piece that’s spring-loaded; its job is to lean or tilt the case toward the ejection-side of the action as the case is withdrawn from the chamber. It’s not commonly possible to encounter a bolt-action that doesn’t have an ejector (custom Benchrest actions and some Long Range Rifle specialty actions don’t).

Ejector Detail in Bolt and Ejector Case Leverage
Here’s an ejector and here’s what an ejector does. Pressure levered against the case will warp the case. It’s a small amount — all these things are small amounts. Case-body sizing helps straighten out the “banana,” that is, a curve in the case body, making it a smaller banana.

Back to the reason I said anything about ejectors in the first place. It makes a banana out of a case. This is unavoidable. The pressure steadily being put against the case base by the ejector warps the case under fire. It’s going to happen on each and every case fired. The bigger the dimensional differences, the greater the warp. Of course, as the uses and reuses add up, the nature of expansion changes. A case can warp one way, and then another way, and then another. Brass has a “memory,” by the way, and we’re always fighting that. Cases tend to follow the same expansion pattern regardless of orientation in the chamber.

There are some, and I’m among them, who think case-body sizing is a good thing to help allay the effects of warped cases, when they return to a correctly-dimensioned chamber. If a rifle chamber is on the larger side, then I honestly think that neck-only sizing may be doing a better job working around it, or working with it, and that’s the primary source of accuracy improvement. I also know that little bit there will get pounced upon.

The “70” on the dial indicator isn’t a measurement of anything; it just happened to be the position of the indicator. What matters is the area the indicator sweeps, measuring points about the circumference of the case. More needle movement means more warping. This pair of photos shows the amount of warp on a new case measured using a V-block-style concentricity fixture with a dial indicator. Even new, they’re not perfect.
The “70” on the dial indicator isn’t a measurement of anything; it just happened to be the position of the indicator. What matters is the area the indicator sweeps, measuring points about the circumference of the case. More needle movement means more warping. This pair of photos shows the amount of warp on a new case measured using a V-block-style concentricity fixture with a dial indicator. Even new, they’re not perfect.

I’m shooting custom-chambered custom-made barrels in my rifles. I do not request “tight” chambers (in any dimension), but they sure aren’t oversized. I like to have headspace set to closely accommodate the case brand I plan to use; doing that minimizes case stretch from the get-go.

Using a concentricity fixture that’s designed to allow isolation of points of measurement along the cartridge, it’s easy to see the warp. Spin a new case, spin a fired case. Some experiment with marking the “high” (or low) point and reinserting the round in the same orientation each time. That’s tedious but possible using a single-shot approach to firing. The point is, that after full-length sizing, I see less runout. I have also seen additional body sizing improve the accuracy of rounds destined for use in rifles with smallish chambers, and that’s one of the first steps many competitive Benchrest shooters take when they’re losing the gilt-edge on groups. For that, they use a die that doesn’t touch anything but the case body.

This pair of photos shows the amount of warp on a fired case measured using a V-block-style concentricity fixture with a dial indicator. As before, the “70” on the dial indicator is just the position of the indicator. What matters is the area the indicator sweeps, which shows they are a little less perfect than the new ones above.
This pair of photos shows the amount of warp on a fired case measured using a V-block-style concentricity fixture with a dial indicator. As before, the “70” on the dial indicator is just the position of the indicator. What matters is the area the indicator sweeps, which shows they are a little less perfect than the new ones above.

If a case becomes a banana, it should be a smaller banana rather than a bigger banana. More technically, it’s a question of if the chambered round can sit in the center of the rifle chamber.

When David Tubb designed the sizing die for his 6XC cartridge, he added an additional 0.0005 inches downsizing right at the case head area. He maintains that is a key to good accuracy at long distance. He’s also setting the case shoulders back 0.002 and running a little more “neck tension” than you might imagine (difference between sized case neck inside diameter and bullet diameter). Tubb maintains that the consistency of case expansion has been an overlooked element in accuracy. Believe me, he’s tried everything, including neck-only sizing, to improve scores at 1000 yards.

And this pair of photos shows the amount of case-diameter variation after they’ve been full-length sized — the variation amount is nearly back to where it started in the new cases.
And this pair of photos shows the amount of case-diameter variation after they’ve been full-length sized — the variation amount is nearly back to where it started in the new cases.

If you’re running a factory bolt-action rifle, by all means try neck-only sizing. If you want to compare results to full-length sizing, just make sure you’re doing that second operation correctly.

Reloaders Corner: Setting Cartridge Case Headspace

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The following is a specially-adapted excerpt from the forthcoming book, “Top-Grade Ammo,” by author Glen Zediker, owner of Zediker Publishing. Click here to order.

by Glen Zediker

A rifle chamber has a headspace; a cartridge case has a headspace. The first is set by the chamber reamer and its operator; the next is up to us on the loading bench.

This is the loose working definition for headspace necessary to understand for this next: It’s the space from the bolt face to the “datum line” on the case shoulder. SAAMI sets standards for this dimension for each cartridge, and a gunsmith or manufacturer can have a little leeway in establishing the exact dimension in a rifle chamber.

In practical terms: Chamber headspace dimensions are fixed; cartridge headspace dimensions are variable. In a semi-auto, there should be some room, space, ahead of the case shoulder when the round is fully chambered, not be a perfect, flush fit. This is necessary for safe function in a semi-auto. In a bolt-action, the difference between chamber headspace and cartridge headspace can be miniscule to non-existent.

A little extra space helps ensure reliable functioning in a semi-auto, and also, mostly, precludes the chance that the case might bottom out on the shoulder area in the chamber before the bolt is fully locked down.

Back to more definitions. A datum line is actually a diameter; the line itself (the point set by the headspace dimension) is the point along a case shoulder that coincides with this diameter. There are only 5 datums that apply to virtually all bottleneck rifle cartridges. (Modern bottleneck rifle cartridges headspace off the case shoulder. Belted magnums and rimmed cartridges are different stories, for a different story.)

To correctly resize cases, we need a gage. Of course we do! I prefer the one shown in this article. It reads from case base to datum line, just as it’s done in chambering a barrel.

I talked before about how semi-autos can often exhibit case shoulder growth in measurable excess of the chamber. Meaning: the case shoulder can be free to expand beyond the confines of rifle chamber dimensions, and that is from the premature bolt unlocking that accompanies most every gas-operated rifle. Even when the system is working optimally, the case shoulder can advance slightly as the bolt just begins to unlock and move away because the case is still containing pressure. The severity of the discrepancy has mostly to do with how much the gas system is overloaded.

To refurbish a spent case, the case body outside needs to be shaped up to near-to-new dimensions, and also the case shoulder needs to be “set back” an adequate amount to ensure positive chambering with just a tad of “rattle” between the chamber shoulder and the case shoulder. In a bolt-gun, the case emerges from the chamber holding essentially a dimensional mirror of the chamber itself (minus, always, the 0.001 “spring back” inherent in the brass material).

For best results, and case life, we need to figure out how much to set the shoulder back. Too much really won’t affect load performance, but, in my belief, deliberately creating what amounts to excessive headspace is not wise. It’s just that much more expansion, that much more “working” the brass has to endure. However! That’s not nearly as bad as leaving the shoulder too high! That’s dangerous.

For day-in, day-out use, I suggest setting back the case shoulder 0.004 inches from fired case dimensions for semi-auto ammunition. If you keep the chamber clean, then go with 0.003. I think that 0.002 is not enough in a semi-auto, but that is plenty enough in a bolt-gun, and 0.001 is the minimum. Commence argument, but I’ll stick by those numbers.

The numbers we need to get from our gage are these: new, unfired case shoulder height (where we started); fired, unsized case shoulder height (where we went to); sized case shoulder height (where we need to get back to).

 

 

 

Case Sizing 1: Sizing Die Selection

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The following is a specially-adapted excerpt from the forthcoming book,” Top-Grade Ammo,” by author Glen Zediker, owner of Zediker Publishing. Click here to order.

by Glen Zediker

Most discussions about reloading tend to center around tools, and the cartridge case–sizing die used to refurbish a spent case is one of the most important. Last time, we were left with a case that had been expanded to the limits of the chamber, plus maybe just a little. The sizing die gets it back in shape for a reuse.

First, I only advise the use of a full-length sizing die for bolt guns or semi-autos. As suggested, a full-length die contacts the full length of the case, the full diameter, from case mouth to case head, and can also contact the shoulder area. There are neck-only dies that, as suggested, only resize the case neck so it will hold another bullet. They don’t touch the case body, and many don’t contact the case shoulder.

As far as brands go, I’m partial to Forster. I like the expander design. It’s located high, so there’s more support about the case when the neck is withdrawn back over it. I still polish this appliance, and recommend always doing so if it’s possible.
As far as brands go, I’m partial to Forster. I like the expander design. It’s located high, so there’s more support about the case when the neck is withdrawn back over it. I still polish this appliance, and recommend always doing so if it’s possible.

A full-length sizer will compress the case body down to the die interior dimensions, which are close to those of factory new ammo. Keep in mind that we’re talking about scant thousandths of inches, but those add up.

Whether it’s a bolt-action, lever-action, semi-automatic, a rifle has to function, and ensuring that cartridges feed into and out of the chamber is the clearly most critical functioning necessity.

If you’re big into or only into single-shots, neck-only sizing is possible, certainly. But even then there’s honestly little to no accuracy or performance benefit from it. The idea is that maintaining the case-body dimensions that more closely replicate the rifle chamber generally tightens up everything and produces better accuracy. Makes sense. But unless we’re working with measurably perfected brass and perfectly concentric rounds and seating bullets to touch the lands or rifling, none of those attributes matter a whit. Any rifle with an ejector is going to warp case bodies, for instance, so the dream of case-to-chamber harmony just can’t exist.

This is a Redding Type-S conventional full-length sizing die. On these, the die interior is pretty much the same as the rifle chamber interior, just a little smaller.
This is a Redding Type-S conventional full-length sizing die. On these, the die interior is pretty much the same as the rifle chamber interior, just a little smaller.

If neck-only sizing was all that influential, then new cases wouldn’t shoot the good groups that they will.

Another thing a full-length sizing die does, or can do, is contact the case shoulder. This is critically important in sizing for repeating rifles.

Last time we talked about what happens to a cartridge case during firing, and it’s not pretty. One of the things that happens is that the case shoulder gets blown forward, which means that if the case were standing up on the bench, that the shoulder will be higher (taller) than it was before firing. To ensure function, and safe function, that dimension needs to be corralled and brought back to what it should be.

To polish the expander, chuck the stem (lightly) in a drill and use a wrap of masking tape to cushion the threads. I first run the edges of the expander over a hard stone to break them and smooth them over, but I don’t run the stone against the body of the expander. Then run it over wet 600-grit emery paper. I use emery paper available at many auto-parts stores. Aluminum-oxide lapping compound works well also. There should be no measurable reduction in the expander body diameter after using the 600-grit paper, but if there is, it’s not going to amount to anything that can have a harmful effect.
To polish the expander, chuck the stem (lightly) in a drill and use a wrap of masking tape to cushion the threads. I first run the edges of the expander over a hard stone to break them and smooth them over, but I don’t run the stone against the body of the expander. Then run it over wet 600-grit emery paper. I use emery paper available at many auto-parts stores. Aluminum-oxide lapping compound works well also. There should be no measurable reduction in the expander body diameter after using the 600-grit paper, but if there is, it’s not going to amount to anything that can have a harmful effect.

There are full-length sizing dies with interchangeable bushings that size the case neck. The idea is to control the amount of case neck reduction, and it also allows the use of a sizing die without an inside-neck sizing appliance (usually called an expander). Good idea. Still, I don’t recommend this style of die for most shooters. One reason why is that there’s a small amount of case neck that doesn’t get sized. Over time, this can create or increase the “case neck donut,” the small raised-up ring of brass that exists inside the case at the case-neck/ case-shoulder juncture. But the die is not the sole cause. Suffice it to say, the additional and inconsistent additional constriction against the bullet isn’t a good thing.

I also do not advocate running a sizing die without an expander or sizing button to control the case neck inside diameter (i.d.). That’s another touted advantage of the bushing dies. That only works well if case necks are perfectly uniform in thickness. Otherwise, it creates off-center case mouths, and ultimately, inconsistency, in bullet pull.

Neck-bushing-style dies (in conjunction with full-length sizing die body) seem like a really good idea, and they can be — but they are another step in controlling case dimensions that most of us don’t want to take or need to take. My biggest issue with bushing dies is that they don’t size the full length of the case neck, and that can create problems. The arrow points to the small area of the case neck that is sized.
Neck-bushing-style dies (in conjunction with full-length sizing die body) seem like a really good idea, and they can be — but they are another step in controlling case dimensions that most of us don’t want to take or need to take. My biggest issue with bushing dies is that they don’t size the full length of the case neck, and that can create problems. The arrow points to the small area of the case neck that is sized.

One of the reasons that the neck-bushing dies came about was from the warranted complaints that conventional sizing dies sized down the case neck outside too much. Most do. Then the expander or sizing button has to open it back up that much more. That’s a lot of stress on the case and the reason for polishing the expander. Another easy fix is to have a machinist open up the neck area in the die. That’s a good idea. I can’t get after the factory techs too much in setting the specs for their dies because they’re trying to cover their bases on all the potential combinations out there, but that doesn’t mean we can’t improve it. There doesn’t have to be more than 0.005 difference between outside diameters and inside diameters to ensure fully adequate sizing. In other words, if the case O.D. is sized down to 0.005 smaller than the measured O.D. after the expander has passed back through, that’s plenty. Check your die by sizing a case without the expander in place. Less is better, but don’t cut it too close; keep room to account for different brass brands, which have different wall thicknesses. This trick will help maintain more material consistency over the life of a case. Otherwise, it’s like bending a piece of metal back and forth until it breaks; the same effect does influence case life when there’s excessive material movement.

One of the best ideas in sizing dies is incorporating a neck-shoulder bushing. These work well because they allow for control over dimensions, including case-shoulder compression, and without the criticisms made against neck bushings. This is a set from Superior Shooting Systems LLC. It’s for 6XC but can also be used, with an appropriate bushing, for .308 Win. Full-length dies with neck/shoulder bushings can control the neck diameter and still get the full neck cylinder sized.
One of the best ideas in sizing dies is incorporating a neck-shoulder bushing. These work well because they allow for control over dimensions, including case-shoulder compression, and without the criticisms made against neck bushings. This is a set from Superior Shooting Systems LLC. It’s for 6XC but can also be used, with an appropriate bushing, for .308 Win. Full-length dies with neck/shoulder bushings can control the neck diameter and still get the full neck cylinder sized.

A small-base full-length sizing die is an option in some die makers’ catalogs. As implied, this reduces the lower portion of the case a tad amount more. I’ve never encountered the need for one in an AR-15. Most have fairly generous chambers, especially if it’s a true NATO-spec. However, I always use one in my M1As, especially when working with a tough case, like a Lake City, that has to fit back into a relatively undersized match chamber. One of the best I’ve used is from Dillon (just the standard die that comes on the Blue machines); Redding also makes a “National Match” sizer engineered just for that rifle.

Next time, I’ll go step-by-step on how to set up a sizing die.

Get looking around this website and locate a cartridge headspace gage, and get it bought. I’ll show you how to use it next time. Either the Hornady LNL Cartridge Headspace Gage or the Forster Datum Dial (shown here) is my recommendation. They both work well. There are also drop-in style gages that will suffice to keep your ammo safe, but won’t give a number to work from.
Get looking around this website and locate a cartridge headspace gage, and get it bought. I’ll show you how to use it next time. Either the Hornady LNL Cartridge Headspace Gage or the Forster Datum Dial (shown here) is my recommendation. They both work well. There are also drop-in style gages that will suffice to keep your ammo safe, but won’t give a number to work from.

 

 

 

 

 

 

 

 

 

 

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Reloaders Corner: The Cartridge Case

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The following is a specially-adapted excerpt from the forthcoming book,” Top-Grade Ammo,” by author Glen Zediker, owner of Zediker Publishing. Click here to order.

Bear with me! We’ll get started on the process of handloading next time when I talk about setting up a sizing die. But before that, it’s good to keep in mind what we’re dealing with, and that is a cartridge case, and also what happens to it during firing, which is what we’re setting out to remedy when we reuse it.

Rifle cartridge cases are made of brass, well, the reusable cases are (they can and have been made from steel and aluminum). There are no brass mines; brass is an alloy composed of copper and zinc and sometimes tiny amounts of other metals, like lead. The mix is usually about 70/30 copper to zinc. Different manufacturers use a different mix or blend, and that influences the nature of the material, and more about that shortly.

When a round is fired, here’s what happens.

When the firing pin or striker point contacts the primer, the cartridge is driven forward into the rifle chamber (as far as it is able to go).

When the primer detonates and its flame enters the cartridge-case flash hole to ignite the propellant, gases are produced that begin to expand the case.

As the propellant is consumed, gas pressure increases, the case head is driven backward against the bolt face, and the case neck and case shoulder are pushed forward as the case neck expands to release the bullet. The case essentially swells up like a balloon to fit the chamber, to the limits of the chamber, and this expansion is in all directions. So the back of the case is pushed into the bolt face and the front area is pushed or blown forward, while, during this, the case body is sealing (essentially sticking to) the chamber walls.

A cartridge case begins to contract just about immediately after it expands. The firing process takes scant milliseconds. Brass is both elastic and plastic. “Elastic” means it will stretch and contract. “Plastic” means it will stretch and stay. The elastic quality makes it expand and seal the chamber and then shrink back enough to be removed or extracted from the chamber. Plastic qualities mean it will also have sustained permanent change. Well, some of it isn’t really permanent because it can be changed again using tools, but some changes are permanent, whether they are literally smoothed over or not. Some cases tend to be harder — less plastic and less elastic — and that is almost always good, or so I say. It’s easy to see that since brass used in a semi-auto has to deal with at least some premature bolt unlocking, a harder composition is less “sticky” in extraction. Even for a bolt-gun, though, harder alloy tends to be smoother cycling. In a semi-auto, case life is strongly influenced by brass composition, and the harder the longer.

Thinking about what happened to the case, what it went through, during firing means we can anticipate the results and effects of dimensional changes. The areas of the chamber that have the greatest dimensional difference between those and the loaded round will have the greatest influence on the dimensions of the spent or fired case. Specifically, the spent case neck will now be too oversized to hold a bullet in place. The case shoulder will have lengthened (elevated if we’re standing the case on its bottom). The case body will have gotten larger in diameter. The case will also have lengthened overall (more about this in another article). What else? Some case material will have moved forward (brass flows in firing) toward the case neck. This material will have come from the area around the case head. The primer pocket will be larger in diameter.

Each firing, brass gets harder overall. In the areas where it expands the most, it gets even harder as it is “worked” through expanding and then being contracted. The tools we use to restore dimensions, the sizing die for good instance, create the contraction. And as suggested, the wall area near the case head gets thinner and the case neck walls get thicker.

All this means quite a bit to the handloader. First, get a clear picture of what’s happened to the spent cartridge case. Essentially, it’s expanded to more closely match the chamber dimensions. Of course, that means different spent-case dimensions from different chambers. Likewise, not all brass cases expand, or stay expanded, in the same way.

Case capacity, by the way, isn’t always as important as it might seem. Greater volume does mean more room for propellant, and expanding gases. With faster to medium propellants, it’s a “trade,” in a way of looking at it. A little less propellant in a little smaller capacity case nets about the same as a little more propellant in a little larger capacity case. Pressure and velocity will be about the same, either way. Now, in larger cartridges, and also often with double-base propellants in any size cartridge, more internal volume will very often mean more velocity at suitable pressure. Point is, don’t worry too much about more or less case capacity in .223 Rem. or .308 Win. I think the alloy composition is more important.

Now we can get started on patching them back up for another use…

Reloaders Corner: Pressure Curves and Port Pressure – Part 2

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The following is a specially-adapted excerpt from the forthcoming book,” Top-Grade Ammo,” by author Glen Zediker, owner of Zediker Publishing. Click here to order.

Last time I gave a caution about respecting one of the differences between semi-auto and bolt-action rifles, and that was with respect to propellant burn rates. The summary reason for that is that different rate propellants will “peak” at different areas as the expanding gases and the bullet travel through the bore. Slower-burning propellants peak farther, and that means more pressure is available at the gas port location in an AR-15, for instance, as the bullet passes it. If the system is oversupplied, then the system is overworked.

Compared to ideal function when gas supply is delivered as engineered, mistimed peak pressures can result in the bolt unlocking too quickly and excessive bolt carrier velocity rearward. The system just gets hit too hard. The extractor tries to yank the case out of the chamber too soon, before the case is released from its grip on the chamber walls (from being expanded through firing). Spent-case condition shows a measurably more abused hull. Probably the worst popular example of these effects is the M1A. I’m doing an entire column or two on reloading for this beast. Essentially, a spent case from an M1A will show dimensions that don’t seem possible. These come from the bolt unlocking too quickly. AR-15s actually handle excessive pressure better than some other designs.

Always keep in mind that this is all happening in about 2 milliseconds. Average time a bullet spends in the barrel, for most modern centerfire rounds, is 0.002 seconds. Timing is everything.

Keeping in mind the behavior of a pressure curve, which is like a wave cresting, factors that influence the amount of gas-port pressure, using the same load, include barrel length, gas-port size, and gas-port location. When the bullet is sealing the bore, the longer the barrel, the more pressure is contained for a longer time. The smaller or larger the gas port size, the slower or faster the gas enters the system. The farther back or forward the port is located, the sooner or later. Bullet weight is a factor also: heavier bullets accelerate more slowly (and also the reason heavy bullets erode the chamber throat more than lighter bullets).

And, the amount of volume inside the bore has a huge influence on all this. That matters when we’re using another caliber than .224 in an AR-15 or .308 in a big-chassis AR (like an SR-25). For instance, in that rifle chambered for .243 Win., but retaining the gas system specifications (gas port size and location) of the .308 Win.–chambered rifle, there’s way more pressure only because there’s less space, less volume, in the bore. The opposite is usually true when we’re running an AR-15 with a larger caliber bullet.

Selecting a propellant with a suitable burning rate, which, again, is something in the vicinity of H4895, is really the only thing we can do on the loading bench to ensure that we’re not contributing to these symptoms. Beyond that, dealing with excessive pressure gets technical.

All my NRA Match Rifles, which usually have 26-inch barrels, get their gas ports moved forward one to two inches. These, of course, are custom-barreled. I also usually install an adjustable gas manifold.

Moving the port forward effectively delays the wave of gas moving through the bore, kind of repositioning its peak with respect to its outlet; there is more space available for expanding gases. It also allows a little slower-burning propellant, which can take more advantage of the longer barrel. It’s common in a similarly constructed AR-10 to get a port moved as much as 5 inches forward to accommodate a .243 Win. or .260 Rem. chambering.

The adjustable manifold allows some tuning. There are essentially two forms these take. One way is to restrict or limit the through-flow; the other just bleeds it off. I like the first kind the best.

Also, I have searched far and wide for a consensus on gas-port sizes, and came up empty.

All this changes with different chamberings and rifle configurations. Carbine-length barrels are particularly sensitive to port pressure because the port is located farther back.

There are a few surefire things that will alert you when your rifle is exhibiting “over-function” symptoms, such as spent-case condition showing excessively blown (extended) case shoulders, extractor marks on the case rim, and a generally explosive sensation in functioning.

In a more extreme circumstance, an over-accelerated carrier can “bounce” back from its rearmost travel so quickly that a round can’t present itself in time to be picked up by the bolt, or the bolt stop can’t engage quickly enough to hold the bolt carrier.

Sometimes what appears to be a “light” load is actually not. I’ve seen excess pressure leave a spent case in the chamber because the extractor lost its grip, and I’ve seen chunks pulled right off case rims. That’s severe. That’s also another cause for the “short-stroke” appearance of over-function: the extractor issue has slowed the carrier.

If you’re having any problems with “over-function,” solutions include retrofitting an adjustable manifold, increasing carrier mass, installing a stouter buffer spring. I do all those things on my rifles. Keep in mind that I am primarily a Service Rifle shooter, and I am trying to push an 80-grain bullet as fast as reasonably possible from a 20-inch barrel that can’t get the modifications mentioned. I know a thing or three about delaying bolt unlocking — I’ll cover more on this topic if you all want to know.

 

Sources:

Sun Devil Manufacturing

663 West 2nd Ave., Suite 16

Mesa, AZ 85210

(480) 833-9876

 

Medesha Firearms Ltd.

10326 E. Adobe Rd.

Mesa, AZ 85207

(480) 986-5876

 

Reloaders Corner: Pressure Curves for Semi-Automatic and Bolt-Action Rifles

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The following is a specially-adapted excerpt from the forthcoming book, Top-Grade Ammo, by author Glen Zediker, owner of Zediker Publishing.

When you’re handloading for semi-automatic rifles and bolt-action rifles, it’s helpful to realize they are not to be approached the same way. Continue reading Reloaders Corner: Pressure Curves for Semi-Automatic and Bolt-Action Rifles

Reloaders Corner: Let Me Introduce Myself

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By Glen Zediker

I’d like to introduce myself, and more importantly, introduce this new regular feature, Reloaders Corner.

I’ve been “at this” for over 40 years now, and “this” is shooting, handloading, and Continue reading Reloaders Corner: Let Me Introduce Myself