by plant_one » Thu Dec 28, 2017 10:32 am
repeated chambering is a valid concern in several firearm types, often for different reasons, but still valid none the less.
in an ar you dont want to load any round too many times under full bolt drop - even in calibers where bullet movement isnt an issue - due to the floating firing pin dimpling the primer over an over. its not usually an issue for a few strikes (4-6) but eventually you will get a slam fire if you do it enough.
for those of us with uppers that have a forward assist, you can mitigate this issue by riding the bolt down with the charging handle slowly and then bumping the last couple clicks to cam the bolt into the lugs with the forward assist. as an added bonus, if you do this right, you can do it very quietly when you sneak into your stand in the morning.
for those with semi-auto pistols, the opposite can happen as we see with our big fat bulelts in the 450 bushmaster, that being bullet setback. as the bullet nose rides up the feed ramp, over time the crimp will fail and the bullet will start to move back into the case. This can lead to a pressure spike if it gets enough setback.
Like with my AR - i rarely will chamber a round more than 4 or 5 times in any of my semi auto's before i cycle it to the bottom of the mag, or put it in the training ammo bin.