Re: Regarding HEADSPACE, what is the
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 308sako</div><div class="ubbcode-body">Maximum permissible amount that would not cause detrimental results?
Not what is ideal, but rather what becomes the threshold of dangerous.
.003", .005", .008" etc. </div></div>
This is a malformed question.
One CAN use a chamber and a cartrige of smaller dimensions to fire form the case from one caliber to aother. In this application, the headspace only has to be such that the firing pin ignites the primer. The powder will take care of resizing the brass. With the low-ish pressures used to fire form, this is a completely safe activity.
For a case that will only see the inside of a chamber once, you can get away with all sorts of big sloppy dimensions. You may even see/hear stories about 308 cases run through a machine gun where the cases are really hard to resize back into tight bolt gun chambers. If the brass is only going to be used once, you may be able to get away with 0.010 (or more) as long as the firing pin can reach the primer and ignite same.
So we come back to the wear aspect. Brass wears by being stretched by firing, and then resized by the resizing die. This effects 3 main areas, the neck, the sholder, and the case just above the web. A bushing die minimizes the work hardening of the case neck, annealing extends the life of the neck. Properly used, these methods can allow the necks to last as long as 50 reload cycles (and more).
This basically leave the discussion with the sholder (position) and the case strech). For brass that is only shot in one gun, minimal resizing is in order, and the cases will attain the correct external dimensions from being fired. after a hand-full of reload cycles, you may have to bump the sholder back 0.002 and get another hand-full of cycles befor doign it again. These cases will have a very long life.
For brass that has to be capable of firing in any correctly headspaced SAAMI chamber, you are not so lucky, and should stick to FL sizing. You will not get the same case life, and this is simply part of the "utility" of a standard (as opposed to an optimized) load.
Finally notice that how stif the load is changes how the cases react. Peak Chamber pressures under 50K PSI can result in cases lasting as long as the necks do. Chamber pressures of 58K PSI still achieve cases that can last 50-ish reload cycles. Venturnign beyond 58K PSI will drop case life rapidly from "quite long" to "a few" in rather short order. Ejextor wipe, punched primers, primer pockets lostening up are sure signs of chamber pressure.
So, with a nice mild load, a case used only once can stand more headspace than most firing pins provide capability to set off the primer it holds.