[Big Bird]

A (civilian) field gauge should be 1.4700. No go should be 1.4670.

The no-go give 0.003 more "allowable error" than the field (or if someone is measuring with a dirty chamber).

A chamber between 1.4640 and 1.4670 has more accuracy potential than 1.4640 to 1.4700 (or military 1.4730). The down side is a tight chamber doesnt have as much tolerance for being dirty.

In a milspec AR the field gauge is the standard. In almost every AR I've handled--including national match rifles with custom chambers--you can push a bolt home on a no-go gauge with some thumb pressure. Spent a day in Gene Barnett's shop a dozen or so years ago when he was barreling DMR rifles for the 101'st Airborne in Clarksville. Every single one he finish reamed would close on a no-go gauge with a little thumb pressure. Not on a field gauge. Reliability is paramount over small gains in accuracy in these rifles. Even in National Match rifles. The tiny degree of increased accuracy you theoretically can get in a tight chamber is easily offset by a loss of 10 points because of an alibi round that failed to fire/chamber during a match In competition at high levels you can't make that up....plus it screws up your mental game which is a big component in rifle matches.

 

[Khufu]

In a milspec AR the field gauge is the standard. In almost every AR I've handled--including national match rifles with custom chambers--you can push a bolt home on a no-go gauge with some thumb pressure. Spent a day in Gene Barnett's shop a dozen or so years ago when he was barreling DMR rifles for the 101'st Airborne in Clarksville. Every single one he finish reamed would close on a no-go gauge with a little thumb pressure. Not on a field gauge. Reliability is paramount over small gains in accuracy in these rifles. Even in National Match rifles. The tiny degree of increased accuracy you theoretically can get in a tight chamber is easily offset by a loss of 10 points because of an alibi round that failed to fire/chamber during a match In competition at high levels you can't make that up....plus it screws up your mental game which is a big component in rifle matches.

There is where you are describing something other than measuring actual headspace.

To actually find head space, you need to take the bolt part (remove the extractor). Then use only the bolt. Once only the bolt is present, determine which head space gauge just allows the bolt to go into the locking lugs and rotate with slight friction (like "drag" on a feeler gauge).

 

[cciman]

More argument, soapbox, tool size, and detail than is needed for this thread.

Best answer to OP question: Use a field gauge to determine if the replacement bolt is safer for use, than not using a headspace tester.

 

[Big Bird]

There is where you are describing something other than measuring actual headspace.

To actually find head space, you need to take the bolt part (remove the extractor). Then use only the bolt. Once only the bolt is present, determine which head space gauge just allows the bolt to go into the locking lugs and rotate with slight friction (like "drag" on a feeler gauge).

Uhhhhh...OK... cutting a chamber to a certain tolerance is how you actually establish headspace. A gunsmith does this with a headspace gauge to check his depth of cut. So yeah its measuring headspace...SMH Also, some headspace gauges do not require bolt disassembly as they are cut to provide relief for the extractor and ejector but obviously some will require you to take the bolt apart...not a big deal either way. I happen to own a USGI Field gauge and it doesn't require the bolt to be taken apart. Either way taking the bolt apart is a 3 minute job and only requires a 1/32 Pin punch.

 

[Khufu]

Uhhhhh...OK... cutting a chamber to a certain tolerance is how you actually establish headspace. A gunsmith does this with a headspace gauge to check his depth of cut. So yeah its measuring headspace...SMH Also, some headspace gauges do not require bolt disassembly as they are cut to provide relief for the extractor and ejector but obviously some will require you to take the bolt apart...not a big deal either way. I happen to own a USGI Field gauge and it doesn't require the bolt to be taken apart. Either way taking the bolt apart is a 3 minute job and only requires a 1/32 Pin punch.

Yes. Disassembling a bolt is easy.

Where the difference that we are talking about is measuring headspace and just saying go / no-go.

As far as go / no-go I haven't seen an AR barrel / bolt combo that has failed that.

Some of my ARs I keep a dedicated bolt to the rifle. The chamber was cut to that bolt.

Other ARs are lego and parts swapped around.