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Originally Posted by WellArmedLiberal
I've read an engineer's analysis once that said a spring under pressure wears out no sooner than a spring under less pressure.
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correct. as long as the spring is not compressed (or extended) past it's intended range of motion, leaving it compressed will not weaken it. cycling it will weaken it. so, ironically, people who unload their mags and cycle them to save the springs are actually wearing the springs out.
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But how many times would a round have to be chambered to start causing setback?
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i think it depends on both the bullet and the gun.
i have done some experiments with a few 9mm bullets. i've tested both 115 gr FMJs and 124 gr HPs. i have rechambered the same rounds in a glock 17 over 30 times and measured no set back at all.
however, i have read of some other similar experiments with .45 ACP where bullet setback was measurable after many fewer rechamberings.
i think one difference might be that the typical .45ACP bullet has a much flatter nose than the typical 9mm bullet. also, i think the .45ACP test was done with a 1911 which, of course, has a different chamber/feeding mechanism from a glock, so that might also factor in.