I recently purchased a 308 barrel on this forum, the person selling made clear that it would need a heck of a shim to make it fit, which it did, not a big deal.
On this one I figured I would try something different.
I cleaned the lug and mixed up some steel epoxy, I filled the under lug with about 1/4" of this 20 minute epoxy. I let it sit for about 5 minutes, and then I sprayed down my frame with WD-40. I then snapped the barrel onto the frame. Pulled it off carefully and cleaned the edges of the lug up with a knife...the extra squishes out.
Let it set up over night, clean the WD-40 out of the frame snap it back together and it is good to go. No wiggle or anything.
Thought someone might like to know that.