AR15 bolts and BCGs - grades of steel


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ThePenguinKnight
May 7, 2013, 05:00 PM
What grades of steel are acceptable for an AR15 bolt and bolt carrier? I understand 8620 and 158 carpenter are common. Is 4140 acceptable? Is it too soft?

What is the minimum grade of steel for an average user? I.e. for shooting <1000 roumds per year, would 4140 be acceptable for the bolt, but not the carrier (or vice versa)?

Thanks in advance.

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silicosys4
May 7, 2013, 05:21 PM
From what I've read, 8620 is acceptable for the carrier, but is too soft for the bolt itself.

Fishbed77
May 7, 2013, 05:58 PM
You want a 158 carpenter steel bolt.

If you are looking to buy, here is what you want in stock:

http://palmettostatearmory.com/index.php/featured/m16-bolt-carrier-group-13009.html

meanmrmustard
May 7, 2013, 06:32 PM
9310, if you can find one.

I find it to have superior qualities to 158, but they're both good.

ThePenguinKnight
May 7, 2013, 10:45 PM
I am looking out of curiosity mostly. Prices haven't come down to where I'm willing to buy anything yet, but I do enjoy researching and learning, and this bit aboutbolt and carrier steel piqued my interest.

I know that 158 is the standard, and likely what I will get when I do buy. That said, I would like to know what the capabilites of the other grades of steel are, if for no other reason than to know.

Any further info, especially pertaining to the effective differences in the steel for these purposes, would be welcome. Thank you again.

Warp
May 7, 2013, 11:07 PM
You want a C158 bolt. Magnetic Particle Inspected (MPI) as well.

I'll follow this thread for more specific information. Usually when this comes up it results in pictures and stories of the lesser-quality bolts failing far more frequently, and easily, than 158, and the only redeeming quality that gets presented for the lesser quality material is that it's cheaper.

I understand a quality BCG is hard to come by/expensive right now. Even before Newtown they were getting expensive and hard to find.

NeuseRvrRat
May 8, 2013, 06:54 PM
everyone has told you what they think you should buy, but not why it's superior

and "the chart says so" isn't good enough

Quentin
May 8, 2013, 07:31 PM
The bolt is a high stress component of the rifle so it makes sense to pay a little more for steel that has a good reputation for strength and longevity. Carpenter 158 steel has that rep over millions of rounds so why save $20 gambling that a lesser steel is good enough? MPI is a good thing as well and of course milspec calls for a proof round first (HP), then MPI.

This is one of the most important areas not to cut corners but up to you, though.

1KPerDay
May 8, 2013, 08:14 PM
So I shouldn't have just bought an 8620 BCG from PSA? Will it go blooey?

Warp
May 8, 2013, 08:17 PM
So I shouldn't have just bought an 8620 BCG from PSA? Will it go blooey?

Probably not. But it does seem, to my perception, as thought it may be more-likely than with 158.

Carpenter 158 has proven itself and was selected for a reason. It's very good at what it does.

I haven't seen anything to indicate that there is a better choice.

meanmrmustard
May 8, 2013, 08:21 PM
So I shouldn't have just bought an 8620 BCG from PSA? Will it go blooey?
No.

Not quite as good as a properly treated 158 or 9310 bolt. But better than either of those if not properly finished.

It'll be fine.

dprice3844444
May 8, 2013, 08:21 PM
try to find one that is mp3 coated,easier to clean

k_dawg
May 8, 2013, 08:38 PM
There is no one 'right' answer. You have to first decide your purpose.

For example, I can stay on target better with the JP Rifles low-mass carrier, even thou it is not 'mil spec'. But that is for recreation/competition/hunting.

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