The proper material for extractor pins is S2 tool steel. The problem is, Carpenter does not make it anymore, unless you order 25,000 lbs.
Because it is so expensive to acquire, it seems most companies substitute S7, which is readily available.
Problem is, S7 is not as strong:
S2 Yield Strength = ~300ksi
S7 Yield Strength = ~220ksi
It is extremely likely that Colt uses S2. I know AAC uses S2. I am not sure who else, but if anyone really wants to know, you can collect samples and pay for testing - that is the kind of thing that could make gun magazines great - if they actually reviewed guns.
I bet the results would be surprising as to who uses what.


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