The best you can use - Precision Armament AccuWasher Gen2 Shim Kit

Finally had to buy my second set in 1/2x28... one of the best MD products out there, and the only I'll use besides JP's double crush washer. Infinitely reuseable, until you lock one in on a barrel. Can be removed and reinstalled with the same MD/barrel countless times. Perfect installment, takes a little more time, but if done right is impossible to screw up. One kit can be used for multiple rifles, and when you run out of the size you need, just buy another kit and combine. If you built lots of rifles, you'll be able to do many with just one or two kits.

I printed out a little 360° diagram and cut a hole in the middle to aid in determining the 10°-30° final tightening/washer. Just follow the instructions and you'll have no issues.

The only negative I could see is the aesthetics, it is a matte stainless washer on a black gun. Would be nice to see sets available in parkerized 4140 steel, if possible, or at least nitride stainless for the cloners out there. Also, woud be nice if a person could buy just one size washer at a time, rather than needing to buy an entirely new kit, but I understand both sides of that argument.

So, if you can add up how many $2-$5 crush washers you've bought and screwed up/replaced, it adds up quick. My first kit allowed me to do a half dozen rifles, including a couple for friends.

Well worth the investment, you won't be disappointed.