AK build with unmatched barrel/trunnion

[Shane762]

I have a Polish underfolder kit (with original barrel) that I purchased about eight years ago. I was thinking of picking up a Nodak receiver this summer and sometime after things calm down having the kit built up. Unfortunately, somehow in the course of several moves I've managed to lose the barrel trunnion. I know that if I look around I can find a Polish trunnion out there somewhere but is it even possible to properly headspace a barrel that's already been installed on a rifle? I'd really, really hate to replace it since it appears the donor rifle had never been fired. There wasn't even any finish wear on it. Thanks.

 

[rob-cubed]

Just to clarify, has the barrel already been drilled for the barrel pin or is it a virgin assembly?

If it hasn't been drilled yet, no worries. You can headspace it to any trunnion.

If it has been drilled, you will likely have to drill the pin oversize to compensate for proper headspacing. How much depends, but if it's a Polish barrel and you get a Polish trunnion we're probably only talking a tiny bit. AK Builder offers reamers and pins in two sizes over the standard 7mm, but if it's just fractions of an inch you might want to sacrifice an old drill bit shank and drill oversize only as much as required. Maybe you'll get lucky and a new trunnion headspaces fine.

 

[Shane762]

Just to clarify, has the barrel already been drilled for the barrel pin or is it a virgin assembly?

If it hasn't been drilled yet, no worries. You can headspace it to any trunnion.

If it has been drilled, you will likely have to drill the pin oversize to compensate for proper headspacing. How much depends, but if it's a Polish barrel and you get a Polish trunnion we're probably only talking a tiny bit. AK Builder offers reamers and pins in two sizes over the standard 7mm, but if it's just fractions of an inch you might want to sacrifice an old drill bit shank and drill oversize only as much as required. Maybe you'll get lucky and a new trunnion headspaces fine.

It has already been drilled. The parts kit was all matching and in pretty much unfired condition so I'm kicking myself doubly for losing the piece.
It never occurred to me that it could be drilled oversize. I was afraid I was going to have to have the area in the barrel welded up and drilled from scratch. Thanks.

 

[rob-cubed]

Guys have welded up pin holes to fix head spacing issues. You will have issues drilling through a weld and keeping everything lined up for the original pin size however. I'd rather do a cold fix, but then my weld skills are splattery at best.

 

[Markp]

The right way is to drill oversize and head space, it's likely going to be very close and so the oversized pin will do the trick.