Getting rid of AR15 upper/lower slop , your preferred method?

[bfoosh006]

FWIW, every SOLGW upper i have, has had a better fit on every lower... good n' tight on a BCM lower through better fit on a PSA lower.

 

[Ichi]

I run the National Match shims in all my AR's. Takes a little time to fit it, but they work great. Nice cheap little kit.

nationalmatchshim

Work in large frames also.
View attachment 8064643

I also use the National Match shims in my ARs. This are the best semi-permanent solution that I've found.

 

[Bluedog82]

I’d be interested to see someone like @Molon test this out as scientifically as possible—say take one of his precision uppers and shoot some groups with it, then throw it on a different lower with the same trigger and shoot a few more groups, then compare.