Shimming a barrel nut


I did a search and can’t find the information on here.

So when putting together a few of my last builds some of the barrel nuts didn’t require shims and some have. Of the ones that have, they always have lined up perfectly for some reason on the first try…

I am doing some reasearch and realized there is some confusion on the placement of the ships. Some guys on YouTube place them between the barrel extension and receiver. Which I tried on my latest and got it to fit much better.

My previous build has them under the barrel but and shredded from being caught in the threads when turning accidentally.

So which is right? And does it matter?


I’ve always put the shims between the barrel and the nut.


Always place the shims between the barrel and the nut. Also, use assembly lube, bring to full or 3/4 torque (I do 3/4 myself) back it off, retorque.
If you have assembly lube, everything works fine. I never take a factory “mil spec” design over 80 foot pounds. I have had units that were torqued well over 125 foot pounds by customers… yeah… bad…
There’s my 2 cents


One of the first ARs I built I over torqued the nut. Yep, destroyed it. After that I started using shims. Haven’t lost a nut since.


So, I am wondering what affect it would have putting the shims on the barrel extension instead of between the barrel and nut.


I would assume increase the distance slightly between the hammer and firing pin


Also the lockup… while very small, small differences add up.