Got a build that has perfect headspace with barrel hand tight but will not close on a 5.56 go gauge once torqued.

Looks like I can get the right size stainless round shims in .1mm and .2mm, to get the right headspace once torqued.

But both the gas port and a slot for the gas block would have to be re drilled and machined to match where ever the barrel ended up clocked at.

Should I go that route or buy a chamber reamer for $105

Reamer route I wouldn’t have to do anything to the gas port or slot.

But I’ve never reamed a chamber. Pretty good chance of screwing up a barrel that is unobtainium.

I don't use go/no go gauges on an AR15. If it fits it ships.

Do Not Shim

It’s an Ar70

You can get all manner of shims from McMaster-Carr.

Why would you need to redrill a gas port that has been displaced a mere .004" to .008"?  

Derp - nevermind.  I read you now.

Do you have a published spec on what the headspace should be for that particular weapon?

Don't know if it will be helpful to you but on chrome lined M14 barrels they will sometimes roll the barrel shoulder to correct timing issues. Some use a hand knurling tool or a modified pipe cutter and others just peen with a hammer. Again, not familiar with what you're working on but just thought I'd put that out there.

I would not do this, sounds like bad practice.

I may be jaded because the one time I had someone install and AK barrel they turned it down too small and knurled it to compensate. I found out when it was jamming and I took it apart to install the correct feed ramp...

OP should buy the reamer.

I've been thinking abou tit's hould be fine to use stainless washers. It's the least invasive solution. And cheapest. You can always cut on it later if it doesn't work.

To get a Mini 14 barrel to index I used a .004 brass shim.  The brass is soft enough to squeeze down and hold the barrel firm.  I had to cut the brass from some sheet stock which took some time since I could not find any to the correct dimensions.  I got this idea from a guy who has spent many years putting barrels on M1 Garands and M1A1's.  

kwg