AR 15 barrel shimming

[striped1]

I am trying to tighten up groups that tend to vertically spread as the barrel heats. I attribute this to tolerance stacking on the barrel extension to receiver fit. I have stainless shim stock to use to shim. My question is do you wrap around to the timing pin and leave a full length space for it or do you wrap all the way around and notch for the pin?

 

[mike cyrwus]

whatever you can do will help. if you can get a proper shim around the whole extension so much the better. if you need to just wedge in a few seperate shims at 2, 6 and 10 o clock, thats good too