I worked my BIL's Stainless 10-22 over, doing most of the things I did to mine and it still didn't shoot worth a darn. We then put a new Stainless bull-barrel from Cabela's on it and suddenly, was fantastic! It wasn't one of the best name barrel brands, but I can't remember what it was. It shot about as well as my Shilen-barreled rifle.
A couple of mods that yielded great improvement were:
1. Filing the sides/bottom of the operating handle and smoothing them so it moves easily in the bolt slot. Years ago, I discovered that this prevents first-shot flyers!!!
2. If the firing pin end is flat and not making deep dents in rims, narrow it up and take a little off the top, so it impacts below the "fold" of the rim because there's no priming compound there and it's taking away from the energy needed to adequately dent the shell. The upper portion of the rim that hits the priming compound area of the rim should be slightly longer than the bottom and the lower pin nose shaped to fan the flame out to the sides. Caution: Don't make the nose of the firing pin sharp...but the edges rounded. You may want to a Google search on Calfee's firing pin modifications.
I don't know how I've lived so many years with only one 10-22, but if you have one that shoots almost 1/2 MOA why do I need another?