Different Bolt for Each AR Upper?

[Jaywalker]

Looking at AR uppers I generally find an offer for a bolt (or bolt control group) with each, and sometimes they're provided automatically. Can one bolt/bolt control group be re-used with all uppers?

Basically, I'm asking if bolts have to be fitted to a barrel/chamber. I understand headspace in the context of a bolt action rifle but not with ARs.

[ASH556]

For a 5.56 NATO spec chamber, there are min and max allowable headspace usually checked with go/no go gauges. The one I have is prescribed by the technical manual to check only for excessive headspace due to bolt wear. If it closes on the field gauge, replace the bolt. Otherwise, good to go.

So theoretically, yes, you could use the same BCG for various uppers. I don’t think it’s a good practice though as the lugs will experience different levels of wear across the different chamber lugs, which could lead to premature bold failure, not to mention it’s probably not best for accuracy either.

Headspace on an AR is ultimately determined when the barrel extension is installed onto the barrel. This is done at the factory and the index pin also indexes the gas port. This is not a user serviceable step, even for an armorer. The fix for bad headspace with AR’s is new barrel and/or bolt.

[Jaywalker]

For a 5.56 NATO spec chamber, there are min and max allowable headspace usually checked with go/no go gauges. The one I have is prescribed by the technical manual to check only for excessive headspace due to bolt wear. If it closes on the field gauge, replace the bolt. Otherwise, good to go.

So theoretically, yes, you could use the same BCG for various uppers. I don’t think it’s a good practice though as the lugs will experience different levels of wear across the different chamber lugs, which could lead to premature bold failure, not to mention it’s probably not best for accuracy either.

Headspace on an AR is ultimately determined when the barrel extension is installed onto the barrel. This is done at the factory and the index pin also indexes the gas port. This is not a user serviceable step, even for an armorer. The fix for bad headspace with AR’s is new barrel and/or bolt.

Thanks, ASH556. I hadn't considered asymmetric lug wear except in the context of headspace.

[voodoo_man]

General rule of thumb should be to have a dedicated bcg for each upper. Some companies use different spec/design bolts and you may need to get a proprietary bcg for that upper if a replacement is needed.

They aren't exactly super expensive, having a mil spec upper which accepts mil spec bcg's is the way to go.