One of the more critical bits of information to percolate out from the massively parallel carbine training efforts in this country is that the bolt in the Stoner pattern rifle has a limited lifespan. Typically, the failure mode is to crack around the cam pin hole. The rifle will continue to operate with a cracked bolt, until the bolt fractures completely in two. Bolts seem to last around 35k rounds in a semi-only 20″ gun, about 20k rounds in a semi-only 16″ gun, to as little as 10k rounds in a 14.5″ M4 that sees a lot of full-auto fire.
If you own an AR, regularly shoot it, and consider it a ‘go-to’ gun in your self-defense battery, I’d like you to take fifteen minutes out of your day today and check your bolt for cracks. Check to see that your rifle is empty, then go ahead and check it again. Push out the rear takedown pin and remove the bolt carrier group. Since you cleaned it right after the last time you shot it (right? Right?), you should be able to easily check it. Under a bright light, visually check the circumference of the bolt around the cam pin hole, then feel with your thumbnail by dragging it fore and aft down the bolt surface. Don’t forget to look in the cam pin hole too. If you have a can of starter fluid or some rubbing alcohol handy, spray that on the bolt. It will quickly evaporate from the surface, but linger in any cracks.
Go ahead and also check your spare bolt for cracks. What, you don’t have a spare bolt? What else do you think goes in the hollow of the pistol grip? Tsk tsk!
While we’re at it, push out the extractor pin and check your extractor spring to make sure it’s not broken, and it has the correct black rubber nub insert installed. If you run a SBR or even a 16″ gun with an M4 length gas tube, a D-Fender d-ring is a cheap piece of insurance.
Now would also be a good time to check your screws holding the gas key on the bolt carrier. These should be staked, but many AR factories do not, or do a poor job. You will need an Allen wrench. If your screws are not staked, find someone with a MOACKS and slip them a tenner to turn the screws for you. Brownells now sells a cheaper version that only runs $70. Don’t bother with locktite on these screws, and for Stoner’s sake, don’t let anyone bang on your carrier with a cold chisel.
If everything checks out, reapply your lube of choice and reassemble your black blaster! Don’t you feel better? I know I do! Please remember to add this little chore to your regular post-practice cleanup and you’ll be very smug indeed when the zombies attack.