Please explain the AR bolt swapping/no headspacing required concept to me.

[El Rojo]

I want to get a 16" upper for the FAB-10 and initially I wanted to get a complete kit so I would have the bolt match the headspace on that barrel. However, there are losts of ARs out there that are a bunch cheaper without the B, BC, CH (bolt, bolt carrier, chargin handle). So what do I need to know about headspacing? I don't think buying headspace guages will help because don't they cost just as much as the B, BC, CH? Thanks for the help.

 

[Redlg155]

As I understand it the headspace dimensions of an AR15 are controlled by the barrel extension usually installed by either the barrel maker or builder (such as Bushmaster).

A properly manufactured AR15 bolt will lock into the barrel extension regardless of the manufacturer provided it is within specs. The bolt has no effect on the headspace because the fit of the bolt locking lugs to the extension is non adjustable and will remain constant. The installation of the barrel also has no effect on the headspace because it is also non adjustable. Just screw it in until it stops. The AR15 design allows forward movement of the bolt until it is locked. It does not have a definite "stop" as would a bolt action rifle.

Using a bolt from a different rifle is generally frowned upon due wear on the engagement surfaces of the bolt and extension and the possibility of not mating up correctly. This isn't an issue with a new bolt.

Buy quality parts from trusted manufacturers and you won't have a problem. Guaging the headspace is up to you, but I personally never worried about it. I just made sure I examined the first couple of rounds out for irregularities.

 

[DMK]

So, if you were to assemble a new upper from brand new parts and it was found that the headspacing was not correct, then there is no way to correct it? Basically it would mean that you would have a barrel (most likely) or bolt (less likely) that was defective/out of spec. Is that right?

 

[ID_shooting]

yup, no way to adjust the headspace. If you are going to build an AR, get a copy of Army TM 9-1005-319-23&P. Look at page 3-47 for head space checking procedures.

 

[Redlg155]

DMK,

Pretty much yes. If the headspace was found to be bad your best bet would be to send it back to the folks you bought it from. You could possibly correct a headspace problem if you had a short chamber with a chamber reamer in a non chrome lined barrel, but I figure it would be a lot easier and cheaper just to get them to send you a new barrel assembly.

You can just hang it up and sent it back with a chrome lined barrel/chamber.

You could always get a tool to remove and replace the barrel extension, but for the average user/builder this has no advantages when it's so easy to get a new complete barrel.'


Good SHooting
Red