Used bolt, new barrel - Gunsmith?

[utahjeepr]

If it's out there's jack to do about it but send the barrel back. The extension/barrel assembly controls headspace.

[AndyLate]

Buy the barrel with a headspaced bolt and a new cam pin. If the smith doing the work is truly familiar with ARs, you should not need to ask them to check anything specific. If they are not it would do no good to ask them.

Andy

[Curlew]

If it's out there's jack to do about it but send the barrel back. The extension/barrel assembly controls headspace.

The barrel assembly is only half of the headspace story — the bolt is the other half. Bolts vary in the distance from bolt-face to the back of their locking lugs. If a certain barrel and certain bolt together fail a headspace check, the problem could be in either one.

From what I’ve read here (@lysander), the M16/M4 drawings allocate a tolerance range of 0.003” to the barrel and another 0.003” to the bolt, for a total headspace range of .006” running IIRC from 1.4646” to 1.4706”.

[utahjeepr]

The barrel assembly is only half of the headspace story — the bolt is the other half. Bolts vary in the distance from bolt-face to the back of their locking lugs. If a certain barrel and certain bolt together fail a headspace check, the problem could be in either one.

From what I’ve read here (@lysander), the M16/M4 drawings allocate a tolerance range of 0.003” to the barrel and another 0.003” to the bolt, for a total headspace range of .006” running IIRC from 1.4646” to 1.4706”.

In my ( limited ) experience it is the installation of the barrel extension that causes the problem. Usually on cheap barrels.

[kirkland]

It sounds to me like the OP has already decided to have a gunsmith do the work. If the bolt looks good with no signs of cracking, and headspaces ok, then I see no reason he shouldn't use it.

[Sports-Ball]

Thanks for all the replies. I'm going to have the gunsmith check the bolt for the issues described here when assembling the upper. This will be a range toy and I'm not concerned about it being duty ready if a failure were to occur. I think worst case scenario I'll have to buy a new bolt if it doesn't pass the checks.

[wanderson]

I see no issue re-using the old bolt

But...

Unless the original bolt is a top tier, PSA has a Toolcraft BCG for $69. If you’re paying someone to swap the barrel, this is cheap.

Keep your original as a spare.

Maybe I missed it, but did the OP run enough rounds to wear a barrel out? Or is this just an upgrade? I rarely see bolts wear out, they just work til they fail.

[Sports-Ball]

I see no issue re-using the old bolt

But...

Unless the original bolt is a top tier, PSA has a Toolcraft BCG for $69. If you’re paying someone to swap the barrel, this is cheap.

Keep your original as a spare.

Maybe I missed it, but did the OP run enough rounds to wear a barrel out? Or is this just an upgrade? I rarely see bolts wear out, they just work til they fail.

I ended up buying a used 6920 and forgot the previous owner's stated round count - I haven't looked at the existing bolt face yet. The rifle looks to be in really good condition. The rifle will be reconfig'd into a block II range toy and as you guys know, these things get crazy expensive. Everything is Colt, used original bcg and new SOCOM barrel going into the upper. Worst case scenario I should be out an extra $100 for a new bolt.