AR Barrel Bore Pin Guage

[markm]

What pin guage(s) is/are best for confirming an AR .223 barrel isn't under-bore?

I'm trying to isolate the reason a barrel is shooting high velocity and popping primers. I measured jump to lands, and that matches a known good (Colt) barrel. So I'm down to tight bore, or non-5.56 chamber.

Pin guages are cheap, so I'd like to eliminate the tight bore possibility before spending the money on a 5.56 Chamber reamer.

SHOULD at .223 pin guage pass through an AR 5.56 barrel??

[markm]

I just ordered 4 pin gauges from .221 to .224. That should cover it well no?

[Hulkstr8]

the pin gauge isn't going to be able to tell if the chamber is cut correctly...

Ned makes a gage that can tell you if it's 5.56 or not. Much cheaper than the reamer too.

[markm]

the pin gauge isn't going to be able to tell if the chamber is cut correctly...

I know that. What I'm trying to avoid is buying an expensive tool that I don't need. So if I pin the bore and that checks out, I know the last possibility is the chamber. I'm 99% sure it's the chamber, but with my luck, I'd buy the reamer and it wouldn't fix my issue.

Ned makes a gage that can tell you if it's 5.56 or not. Much cheaper than the reamer too.

I would buy the gauge if I ran across a lot of problem barrels, but I just have the one.

[Todd.K]

There is also bore area, that is part of the SAAMI print. It needs the bore and land diameters, as well as the land and grove ratio to calculate.

It is a better way to measure the size of the hole the bullet goes through for pressure concerns than the land diameter, but it’s not something that is easy to measure.

[the AR-15 Junkie]

I just ordered 4 pin gauges from .221 to .224. That should cover it well no?

None of those will fit, to large.

[joedirt199]

There is that metal stuff that you can melt into the chamber and bore to measure what is going on. Can't remember what it is called but it is low temp soft then hardens when cooled. I have an ingot of it but never used it. It is for making chamber casts.

[Dr Dues]

Been there Mark.....

I understand your trying to save money, but Neds' 5.56 reamer is more then worth the scratch! I've found 6920 barrels that were short (probably end of reamer life).

The only way I know of easily (a relative term) finding bore diameter is slugging the barrel. I've done this and it was a real pain; and didn't really help much.

YMMV

[markm]

Thanks, all! Yeah.. I've read about chamber casting and slugging. Both were too much ass ache for me as a non-gun smith. My reluctance is due to the barrel being contracted for the Mil. BUT... perhaps the barrels were rejected for this reason. Who knows the real back story on "over-runs".

Looks like I'm just going to have to get the reamer.

[Ned Christiansen]

A .219 or .218 pin ought to fit. My bore erosion gage is .220 so it is basically detecting any erosion of the bore diameter to .220 or greater.

If you have a bore scope, and with all the things you do I think you oughta, you can use it to detect a short freebore / throat.