Coronach is right.
Mil-spec bolts do fail and the majority of the bolts are used on, gasp, Colt produced M4 carbines that are heavily used on the full auto setting.
M16A1 and A2 rifle bolts fail at a much lower rate.
I was a Small Arms Repairman during the late 1970s and early 1980s and I have seen and repaired rifles with bolt failures.
These were all M16A1 rifles and god only knows how many rounds were fired through the rifles before the bolt finally broke.
The bolts that really failed always broke at the cam pin through hole.
I have also seen bolts that blew the extractor assembly off the bolt and sheared the bolt lugs in the extractor area.
The bolt failures occurred in Colt, Harrington Richardson, and Hydramatic made rifles.
The Harrington Richardson made rifles seemed to be the most prevelant rifles that had bolt failure issues.
The interesting thing is that CAR15 rifles or M177A1 carbines also came into the shop for repair and I don't ever recall one that had a bolt failure.
These carbines were all, gasp, Colt made.
Civilian commercial bolts fail, no doubt, I have also repaired a couple of rifles with bolt failure.
It is my opinion that given the much reduced stresses on a semi automatic rifle bolt, these failures should not have occurred, at least they should not have occurred at the claimed number of rounds fired through the weapon.
I have an observation, don't know if it means anything or not.
The commercial bolts that I have seen that failed all appear to have not been machined correctly in the cam pin area.
Put them back together and the cam pin would slide into the hole from the top or the bottom of the bolt.
A correctly machined bolt will not allow the cam pin to enter the bottom hole, it is intentionally machined smaller to prevent someone from inadvertantly installing the bolt into the bolt carrier backwards.
At first I thought this was just due to distortion of the metal due to the breakage until I checked out a few bolts from the source where these bolts came from and they had the same issue, cam pin would go in from the top or the bottom.
The additional metal removed to allow this to occur may have weakened the bolts enough to allow them to fail with moderate use.
Another observation I have is that I have not ever seen a commercial bolt that has failed at the extractor as the M16A1 rifles were prone to do.
I have been working on commercial AR15 rifles since 1989.
In almost twenty years of working on these rifles, and I mean a bunch of AR15 rifles, from just about every big name company out there as i do work for guys who shoot competetively, I have repaired two, maybe three, rifles for broken bolts and none with a sheared extractor.
I know bolts fail.
I am pretty sure bolts fail at these Tactical shooting schools because they subject the rifles to the same types of abuse that causes bolts to fail in the military.
I also feel the subject of bolt failure may be a bit overblown for the average shooter, and by average shooter I mean the guy who is shooting 1500 to 2000 rounds a year through his rifle.
As for Carpenter 158 steel, it is better stuff than one might think and while it is 60s technology and better steels could be utilized for bolts, I highly doubt the Government is going to spring for new bolts for every single rifle in the inventory, provided they would spring for the Research and Development money to prove there is a better bolt steel in the first place.
Carpenter 158 bolts are good, they do the job, and they are cheap to replace.
If you stay awake at night worrying that your rifle bolt is going to fail at the most inopportune time, I have a couple of suggestions.
1. Carry a back-up handgun and practice with it.
2. Buy a Magpul MIAD grip, install it on your rifle and get the grip core designed to keep a spare bolt and firing pin, buy a spare bolt and firing pin, keep this grip core in the grip at all times.
3. Buy a bottle of Sominex and get some sleep, you worrry too much.
, but i have seen several AR bolts just go SNAP! and break. Wouldn't it also improve the AR's ability to stand more bolt thrust? It would be pretty simple to use a metal more suited to this application than carpenter 158, wouldn't it?
