I am in the process of building a custom AR for a friend who's son is (hopefully) soon to be returning from sandy far away places, and I would like to get some input on bolt selection. I would like to know what is the difference between a bolt constructed from 8620, 9310 or one from Carpenter 158? I've heard that JP Rifles carries a bolt by Leitner-Wise Defense that is made from 9310 and is extremely tough. Anvil Arms carries bolts made in 9310 or Carpenter 158 as well.  So...... What would be the best choice to put in a SHTF gun and why?

Thanks in advance for any input and advise.....


Also, is Carpenter 158 the Mil-Spec for bolts or is 8620? I've seen it called out as both on different sights.

9310 material is used for a few reasons

It's sold in round stock and it can be hard turned. It also is a high nickle steel and can be chrome plated with less issues with breaking. Because of its high nickle content it is less brittle.

158 is the material that is Mil Spec and its as good as 9310 AS LONG AS the company buys alot of this steel because a company would have to buy a whole mill run of this to even be able to get some. This makes it tough for companies to buy it unless they plan on being a Colt size mil spec supplier/contractor.

158 Mil Spec which means 158 material is on the TDP but as soon as the next TDP holder submits this material change to 9310 the US Government will accept it, because there is not any durablity or function change.

158 is cheaper but 9310 can be purchased in lower amounts, which for most manufactures is even more important.

6 of 1 half dozen of anouther.

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PursuitSS

Interesting reading in the link....... Think I'll maybe try Anvil Arms.

Try Bravo Company.  Best BCG for the $ out there.

Who is the next TDP holder?  Colt owns both TDPs (M16 and M4) and licenses them out.  

Colt no longer owns the TDP for the M4, the US Military now holds the rights.

PursuitSS

Nope.  Colt still owns both of them.  Colt's sole source contract expired.  Currently they are still producing the M4.  All this means is that the Military can seek other soucres for the M4 besides Colt.  Just like FN with the M16 contract.  Bottom line is Colt owns the TDPs and licences them out to the Military and FN.

Sabre Defence also holds the M4 TDP

AFAIK they haven't started production on that contract yet, though.