I will try this again, my first in depth response disappearred.
I suggest shooting the gun as is before you go changing anything. Not all guns need the o-ring trick. Some guns shoot better without it. Unless the forearm is putting uneven pressure on the barrel, in whichever setup you are using, either with or without the o-ring, you should not have to sand the barrel channel in the forearm. Remember, KISS, and only change one variable (thing) at a time when you are checking and setting up your gun for accuracy so you will know what works and what does not...best of luck....<><....
