Month: December 2007

Case Life

Posted by on December 18, 2007

While ruminating about this and that I got to thinking about case life. It could be argued that if you get 15 rounds out of a 308 case, cost per round is so low that there’s not much to be saved by extending it to 20 or 25 rounds. In any case, my interest is what happens if brass is not available ? So it is worth exploring I reckon.Rifle cases usually fail by splitting at the neck, but neck tension has become too weak by then anyway. They fail at the neck because brass hardens and gets brittle by working, and the sizing and expanding that causes work hardening is most violent at the neck. Rifle case necks are first sized down then expanded back up to the required size by the expander plug. Sizing them down and then up again work hardens them a lot. So why not just size them down to the diameter required and dispense with the expander plug ? Because of tolerances in cases. The die maker doesn’t know what the case wall thickness will be, so he must make his dies to handle the thinnest walls likely to be encountered. If he doesn’t, his dies will not size thin walled cases far enough to hold a bullet. Dies are therefore all made on the tight side. The result is that all cases, and thick walled cases especially, are sized too much, and the only way to get them to end up the desired size is to fit the die with an expander plug.I have some Sako 308 cases fired in my rifle and some PMP cases fired in another rifle. The Sako necks all measure 0.404 OD and the PMP all 0.406. Cases expand to fill the chamber when fired then shrink slightly because of elasticity or “spring” of the brass. The small difference in these cases shows only that the chamber necks of the rifles are slightly different, which is to be expected.I use both RCBS dies and a Lee Target Model Loader. The Target Loader neck sizes only, and the necks, when captured in the sizing die, are reamed with the reamer that is part of the Target Loader kit. The case necks are thus uniform in thickness and concentric. The sizing die reduces the neck to the desired diameter, ie there is no expander plug..I sized a few fired cases that had previously had their necks uniformed as described above with both the RCBS dies and the Target Loader. After sizing in the Target Loader neck OD is 0.397. After sizing in the RCBS die it is 0.398. Pretty much the same which is to be expected as that is about the diameter needed to grip the seated bullet. That tells us that the amount of normal sizing required is 7 – 9 thousandths. The interesting point, however, is that cases sized with the RCBS die without it’s expander plug are 0.390 OD. Therefore, in addition to 7 – 9 thou of normal sizing the RCBS die is taking them down another 8 thousandths, and to make matters worse is then stretching them up 8 thousandths.The amount of working of the brass is therefore three times as much in the RCBS dies as in the Lee Target die. The solution ? I reckon it is a good idea to lap the die neck out to the diameter that will size the necks to the same diameter that is presently left by the expander plug. In the case of my 308 that would be 0.398, ie an enlargement of 8 thousandths. Obviously it would differ slightly from other rifles, dies and brass. I have not yet done it but I plan to.Of course, neck life can be extended by annealing, which I recommend. But it is not a matter of either/or, as both these methods can be used. I have no info as to how much this will extend case life but I suspect that it will be quite a lot.Something else to bear in mind, not directly related to the above, is that cases with split necks are not necessarily useless. All cases with the parent 7 x 57 head can be made into shorter cases like 45 ACP and possibly others I haven’t thought of. Some of this forum will be aware of the 458 x two inch which is simply a 458 Win shortened for use in LA carbines. MV is under 2000PS but still greatly exceeds old calibres like the Martini Henry and don’t forget that the MH was effective at ranges well beyond 300m. Any of the belted magnum cases can be used for the 458 x two inch.Case conversion is a topic all on it’s own, but there is hardly a cartridge that can’t be made from another, and hardly a case that can’t be altered to another calibre. The lesson ? Don’t throw away brass, even if it’s a calibre you don’t shoot, or even if the neck is split. You never know when you or someone else might need it.Same goes for berdan brass. It can be converted to boxer.[Originally posted to SATalkGuns -- Admin]

Jacketed Bullets

Posted by on December 11, 2007

I might have mentioned that my buddy Richard B has made bullet dies. He said they were only experimental to prove the viability of making the dies and the bullets and were thus a bit crude at this stage. Today he showed me some 243 bullets he made from 22RF cases and some 30 cal jackets drawn from an old hot water geyser. As he said the bullets were not perfect, for example they had a slight annular depression where you’d find the extractor groove on a rimless case. That’s due to some imprecision in the drawing die. As he said, it’s just a matter of matching the die exactly to the 22 cases. But they were good enough to shoot, and he fired some with respectable accuracy in the circumstances.The 30 cal jackets were drawn from discs cut from a hot water cylinder. They were longer than needed and were very nice, no cracks or splits despite having been annealed only once before the first draw. Because of that, the corners of the bases were quite generously rounded. But that was the only fault if it can be called a fault.The quality of both was such that he has proved the viability of drawing jackets and making bullets, and making the dies to do it. There seems to be very little to do with firearms and ammo that can’t be done by amateurs if the will is there. Now, who knows exactly, from actual experience, how to make primer compounds and propellants ?[Originally posted to SATalkGuns -- Admin]