Used bolt, new barrel - Gunsmith?

[Sports-Ball]

I'm planning on having a used upper rebuilt (with unknown round count, though looks newish) with a new barrel. I'm going to have a gunsmith do the work and I'm not exactly sure what to ask him to do in order to check that the new barrel and used bolt are compatible. I'm vaguely familiar with the idea of checking headspace, is that what I need to ask him to do? Any other checks I should have him perform?

[GH41]

If you get both bolt and barrel from reputable suppliers headspace shouldn't even need checking. I wouldn't put the used bolt back in as cheap as quality BCGs are.

[markm]

Agreed. Unless one of the parts is really worn looking, you're fine assuming they're good parts to start with.

[Evil Black Rifle]

Have the gunsmith check head space, or buy your own barrel changing tools and head space gauges.

[grizzman]

I suggest using one of your new spare BCGs with the new barrel.

If you don’t have a new spare BCG, then buy a new BCG for the new barrel and make the used one an emergency spare.

[gunnerblue]

Rebarreling an upper isn't really gunsmithing, any reason why you don't just do it yourself? Headspace gauges are inexpensive

[DG23]

If you get both bolt and barrel from reputable suppliers headspace shouldn't even need checking. I wouldn't put the used bolt back in as cheap as quality BCGs are.

Agree about replacing the bolt along with the barrel but...

I would keep / reuse the same carrier he already has if it is in good condition as it is already mated to the upper he is reusing.

A new carrier is going to add a lot of wear to his used upper (while it becomes mated) for no good reason. The one he has already likely has a lot of miles left in it before needing any attention.

[utahjeepr]

^^^ This. A new quality bolt is cheap, keep the old one for a spare.

AR headspace ain't much of a thing. I have gauges so I use em but... I would imagine your smith will too, just cuz.

[georgeib]

^^^ This. A new quality bolt is cheap, keep the old one for a spare.

AR headspace ain't much of a thing. I have gauges so I use em but... I would imagine your smith will too, just cuz.

Agreed. By the time you've paid a 'smith, you could have just bought a new bolt and popped it in. That's what I'd do.

[lysander]

If its out, what are you going to do? What can a gunsmith do in this case that you cannot?

[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.