![]() ![]() I am not so sure that all pistol brass "shrinks" upon firing, or if it does, that it will continue to do so after several firings. Exceptions would be some magnum revolver rounds which do seem to require trimming after a variable number of firings depending on the pressures generated and the ductility of the brass. ![]() Since the brass "releases" itself a lot quicker than a rifle case, it does not normally get stretched like rifle brass, and so we don't normally have to trim them. Headspace in auto pistols is a lot less critical than that of rifle chambers, as the pressures generated are not nearly as high. At this point there is still enough pressure to force the case backwards into the breechface and start the slide to move rearward. All primers move a bit during firing, only to be hammered back into place as the case proper frees itself from the chamber as pressure in the chamber is reduced after firing and it contracts or springs back to a smaller diameter. If the headspace is too great, the primer will back out too far during the firing cycle, impaling itself deeply with the still extended firing pin, thus causing a rupture. The real limiting factor is whether the firing pin can hit the primer, have enough energy to set it off, and not puncture it. 744, but few cases in the various calibers in auto pistols actually measure the minimum dimension when new. ![]()
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