Inspired by a thread on another forum, I decided to take a new round of my carry ammunition and chamber it multiple times to observe the effects on the OAL of the round. I used a recently recalibrated Mitutoyo digital caliper. The weapon tested was a relatively new Steyr M9A1 with probably just a hair under 1000 rounds through it. The barrel was replaced by Steyr a few months ago and probably has about 300 rounds through it. The ammo tested was new Winchester Ranger 127gr. +P+. I measured quite a few new rounds and found the OAL varied roughly .05mm. So, on to the testing. Each time, I took an empty magazine and loaded the round. I inserted the magazine and used the slide release button to chamber the round. When I began, the OAL of the test round measured 28.27mm. After being rechambered 20 times, the OAL measured 28.22mm. Rechambering the round did indeed make a small difference of .05mm. The bullet was also notably scratched. I will probably perform this test again in the next day or two on a few more rounds, and I will post the results. So now comes my question to more knowledgable members: is this .05mm difference in length going to make any difference in the chamber pressures? I would certainly assume not, as that is the exact length the different bullets varied in the pack. Thanks guys!