AR Bolt - Carpenter 158 or 9310?

bigfutz · Jul 25, 2013

I know Carpenter 158 is Mil Spec for AR bolts, but I've been seeing quite a few for sale online advertising 9310 as being "better." What say ye?

94formulabird · Jul 26, 2013

Think I read somewhere that 9310 was stronger...but more likely to break wit alot of abuse due to 158 having some give

Paco · Jul 26, 2013

From ARFCOM's archives:

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 another.

Carpenter 158 is only produced by one company (hence "Carpenter") whereas 9310 is a standard steel type.
FYI: 8620 steel bolt = garbage.

bigfutz · May 23, 2014

Here's an excerpt from JP Enterprises

The truth is, the standard Mil-spec C-158 (Carpenter 158) bolt has a number of factors limiting its performance, not the least of which is that the life expectancy of such bolts is only about 6,000 rounds. In fact, standard bolts will start to show stress cracks on the locking lugs adjacent to the extractor cut after only 3,000 rounds. Cracking at the cam pin hole and weak extractor spring tension only add to the problems of the Mil-spec bolt.

...

The material used in these standard bolts is also not the best choice by today's standards, but if you remember the old story that explains why ?Mil-spec never dies,? that applies here as well; they make them this way because they?ve always made them this way.

The latest edition JP EnhancedBolt? is made from SAE 9310 high-grade steel. This material makes for an extremely hard surface with a tough, ductile core resistant to structural failure and a life expectancy far exceeding Mil-spec C-158 bolts. SAE 9310 is the same type of steel used in the transmission gears of Formula One racecars, and the high-load application of a bolt assembly is ideal for this state-of-the-art material; the results of actual full-auto endurance torture tests prove it.

http://jprifles.com/1.4.7_bc.php

Tigerstripe · May 23, 2014

those guys are just trying to sell you on their expensive products.

until this month i have had the same bolt and carrier in my full auto rifle .

i am sure i have fired over 10,000 rds and it could be as much as 15,000.

it is probably carpenter 158 so i dont see a need to worry about a semi rifle bolt.

edit.

maybe i havent fired that many rds. i have reloaded a lot but havent fired them all.

it has fired 6000 or more of mine and however many others have put in it.

my point is, i dont think there is much to worry about especially in a semi.

bigfutz · May 25, 2014

my point is, i dont think there is much to worry about especially in a semi.

My point exactly. IOW don't fret if it's 9310 and not C158 "milspec." I have seen some that are 8620 (same steel as the carrier)... I don't know about that.