Extractor pins

[rsilvers]

There are materials which can meet or exceed C158 now, but they are just as rare and costly. I have spoken to Carpenter about 9310, which they also manufacture, and he did not consider it to be as good for this particular application (even though it is good for transmission gears, which have a different failure mode).

The AR bolt is the weak link in the rifle, so one should use the best material - and also one should not open the bolt face for 7.62x39mm.

[Spooky130]

I had an extractor pin fail on an old Olympic Arms rifle. Snapped right in half and the rifle stopped working…

[Suwannee_Tim]

@An_Undocumented_Work

…I mean surely metalurgy has advanced since the 50’s

I think it has but not by a lot. Metalurgy was pretty a pretty mature technology in the '50s. Then, ferrous metals had been under intensive scientific investigation and improvement for over 100 years.

@rsilvers

…The AR bolt is the weak link in the rifle, so one should use the best material - and also one should not open the bolt face for 7.62x39mm.

Or .450 Bushmaster? Which is why .450 BM operates at pressures typical of pistols.