Fireforming Brass

An Important Technique For A Handloader To Learn.

Cartridge brass is about 70-percent copper and 30-percent zinc, a relatively low-cost alloy that’s easily softened (annealed) by heating or hardened by “working” to enhance certain characteristics. The relatively thick head of the case is left work-hardened after manufacturing to contain pressures, but the front end of the case is annealed to remain more flexible. This flexibility helps the neck hold a bullet firmly, and also allows the thin walls of the case to expand during firing, sealing the chamber against gas blowback, then contract slightly after pressure drops to allow extraction.

This flexibility also allows rifle addicts to create new cartridges. If the rifle’s chamber is reamed larger, the brass case will expand to fit the new chamber. This fireforming is usually connected with wildcat rounds, with steeper shoulder angles and less-tapered bodies capable of holding more powder. But blowing-out brass has also created new factory rounds: The .300 Weatherby Magnum is an improved version of the .300 Holland & Holland, and Nosler recently legitimized the .280 Ackley Improved, a popular wildcat (see February 2013 issue). Sometimes fireforming can also be used to turn cheaper factory cases into other factory cases that might be scarce or expensive, so any avid handloader should be familiar with various fireforming techniques, as well as potential problems.

The biggest problem is maintaining headspace. A slight amount of excess headspace results in case stretching, or even separation near the case’s head. Rimmed and belted brass can be fired without any worries, but the firing pin can drive rimless brass a little too far into the new chamber, shortening the head-to-shoulder distance.

Most rifles re-barreled to improved rimless cases have the chamber set up for a slight crush-fit with factory brass. New cases have a slight radius between the neck and shoulder, just enough to help maintain this crush-fit against the firing pin’s blow. If your rifle’s set up this way, all you have to do is fire factory ammo or full-pressure handloads in new brass, and the improved cases will come from the chamber perfectly formed.

Many handloaders, however, are tempted to save money by using reduced loads to fireform cases, often combined with cheaper cast bullets. But if pressure isn’t near the SAAMI maximum for the parent round, the case heads might not be driven back firmly into the bolt face, and some cases can still end up with a slight amount of excess headspace, even with a crush-fit chamber.

Unless you plan to segregate cases for use with reduced loads and/or cast bullets, fireform with a full-power load using jacketed bullets. Since we’re handloaders anyway, most of us will fire handloaded new brass, and a maximum load for the parent case will guarantee complete expansion of the improved case.

handloading 1

The most enjoyable way to fireform a bunch of brass is prairie dog shooting (above). Rimless cases like the .35 Whelen (below, left) need to either firmly “crush-fit” in an improved chamber, or have the bullet seated out to firmly meet the rifling to properly fireform. Rimmed or belted brass can simply be chambered and fired, as Roy Weatherby did when transforming the .300 H&H into the .300 Weatherby Magnum (right).

handloading 2

New Brass best

It’s not absolutely necessary to use new brass, but it works best for a couple of reasons. First, firing work-hardens brass, especially the thinner body and neck. If the brass has been fired more than once or maybe twice, it can crack during fireforming. (Work-hardening is also why it’s a good idea to anneal brass after fireforming, since the extra stretching to fill the new chamber walls work-hardens brass even more than normal firing.)

Second, when new rimless brass is fired the first time in standard chambers, it loses that slight radius between neck and shoulder, so doesn’t headspace as firmly when chambered in a crush-fit improved chamber. As a result, case stretching or even misfires can result.

I once went on a prairie dog shoot with a friend who brought a brand-new custom rifle chambered for an improved cartridge. This is a really good way to fireform a bunch of brass, but about every fifth round from Joe’s new rifle wouldn’t go bang. He started cussing the gunsmith, but I interrupted the blue streak to ask if his handloads were in fired brass. They were—and once he got back home and switched to new brass the misfires disappeared.

Misfires also tend to occur when an improved chamber isn’t reamed for a new-brass crush-fit. This often happens when somebody runs an improved reamer into the chamber of a factory rifle.

Chamber Cure

The right way to create an improved-chamber on a factory rifle is to unscrew the barrel and remove one thread, shortening the chamber just enough so the improved reamer results in a crush fit. But removing the barrel and cutting off the thread involves extra time and skill. As a result most amateur (and even some professional) gunsmiths bypass the extra work. The chamber sometimes ends up too long for reliable ignition, and rounds that do fire end up stretched.

The solution is to seat the bullets into the lands, keeping the case head firmly against the bolt face. Bullets seated into the lands increase pressures, so a starting load for the parent case should be used. This is also a handy technique for fireforming brass to the generous chambers of some old military rifles.

Occasionally the case-neck doesn’t grip the bullet firmly enough to keep the case from being shoved forward, especially from the heavy firing-pin blow of, say, a 98 Mauser. One solution is to remove the expander ball from the sizing die, leaving the case neck smaller so it grips the bullet more firmly. Crimping the bullet can also help.

If the headspace is a little long but cases will still fire consistently, oiling the case will allow it to slip rearward without stretching. No, this doesn’t increase bolt-thrust. Any suitable oil loses its lubricity at pressures below 10,000 psi. Once pressure rises to 10,000 psi, the case grips the chamber wall firmly.

handloading 3

The cheapest way to fireform cases is with a little fast-burning powder topped with Cream of Wheat, above (or other coarse-milled grain). John used the COW method to transform .22-250 cases into 6.5 Creedmoors.

Bullet Free

If you really want to save money when fireforming, go bullet-free. There are a bunch of variations, but perhaps the most common is sometimes referred to as the COW (Cream of Wheat) method. Instead of a case full of rifle powder and an expensive jacketed bullet, use a small charge of really fast-burning powder, then fill the case with uncooked Cream of Wheat. (I use a generic version, saving a few more pennies.) The cereal is usually topped with something cheap and expendable, to hold the round together. I usually use a wadded-up cotton cleaning patch stuffed inside the case neck, but a paper or wax plug also works. Or, if you can load the round into the chamber with the barrel pointed up, a neck-plug isn’t necessary.

Some experimentation is usually required to find the exact load to fully form the case, without rounded shoulders or excess headspace. A couple of years ago I used the COW method to fireform 6.5 Creedmoor cases from Winchester .22-250 brass. (The Creedmoor case is essentially the .250 Savage Improved necked up to 6.5mm.) It took half-a-dozen rounds to find 18.0 grains of Alliant Unique formed the cases perfectly, but switching to another case and powder would require another test trial.
By John Barsness

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GUNS May 2013

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3 thoughts on “Fireforming Brass

  1. jason

    Do you have any info on fire froming a 300 win mag to a 6.5×68 any info on on the 6.5×68/300 would be great on on hand loading they don’t make ammo for this round so I have to make it using 300 win mag brass and I can find any load data .thanks


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