7.62x39 barrel issue

[czgunner]

I decided to put a cheap(ish) 7.62x39 upper together. I bought a KAK 11" barrel that is advertised as having a .311" bore. I assembled the upper this afternoon. Before shooting through my YHM ULT, I checked alignment with my Suppressor Alignment Gage, which measures .295". The gauge will not drop in from the muzzle end. It gets stuck in the barrel if inserted from the breech. I thought I had an issue with my YHM mount, so I pulled that and no dice. The barrel won't accept the gage.
My AR10 in .308 and my 300 BO both readily accept the gauge.
I sent an email off to KAK, but was wondering if anybody here has any idea what may be going on. Did the rifling tool wear out 1/2 way down my barrel?
This is the muzzle here, not accepting a 7.62x39 bullet. The point at which the bullet stops in the barrel measures .291"

[Arik]

I'm not sure the bullet is supposed to go down to the case neck. I've never had a AR in that caliber but all AKs I've had looked like that last picture.

I'm pretty sure if the case neck was touching the muzzle you'd have a shot out barrel

Here's my 7.62 AKSU that I've owned for 10+ years

Attachment 65119

[czgunner]

I'm not sure the bullet is supposed to go down to the case neck. I've never had a AR in that caliber but all AKs I've had looked like that last picture.

I'm pretty sure if the case neck was touching the muzzle you'd have a shot out barrel

Here's my 7.62 AKSU that I've owned for 10+ years

Attachment 65119

I agree it shouldn’t swallow the bullet. Just included the picture for reference. I just don’t get how my gauge (.308) drops into my 300 BO barrel (.308) and won’t drop into this barrel (.311).

[Bret]

I checked alignment with my Geissele gauge, which I'm assuming is .308

You need a caliper. You don't want to assume anything when it comes to thousandths of an inch. I do of course see your point.

[czgunner]

You need a caliper. You don't want to assume anything when it comes to thousandths of an inch. I do of course see your point.

I’ll dig one out, but how does it drop into my .308 and 300 BO barrel and not this barrel?

[czgunner]

OK, I'm getting some bizarre replies. Not sure I made myself clear or people aren't understanding what's going on.

I know that the barrel isn't supposed to accept the bullet. The picture was added for a point of reference. The muzzle stops the bullet at .291"

I measured the Geissele rod with my caliper and it is .295". So, there is a problem if the supposed .311" bore barrel can't accept a gauge that my .308" bore rifles can.

[Bret]

I’ll dig one out, but how does it drop into my .308 and 300 BO barrel and not this barrel?

It might just be that the lands are taller on the 7.62x39 barrel. The grooves determine the internal diameter of the barrel.

[czgunner]

It might just be that the lands are taller on the 7.62x39 barrel. The grooves determine the internal diameter of the barrel.

OK, thank you.

[AndyLate]

Yes, 30 caliber refers to the bore measured at the top of the lands and 308 (or .311) the bore measured at the grooves. It will be interesting to see what KAK says. The funny thing is that if the throat is large/long enough, you may have never known if you assembled it and just shot it.

You can download the SAMMI rifle cartridge and chamber drawings (one .PDF) here: https://saami.org/wp-content/uploads...sting-Copy.pdf

Andy

[czgunner]

KAK wrote back and advised that it’s probably fine. I should break it in first before mounting the can. Odd response. I took a shot and it locks back and nothing blew up.
Using these janky Ross uni mags.