GUNS Magazine May 2013 Digital Edition - Page 13

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 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 .22250 cases into 6.5 Creedmoors. 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. 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. W W W. G U N S M AG A Z I N E . C O M 13

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