I have built 5 10/22's with commercially available parts and high powered scopes. They shot very well easily under 1" @ 100 yrds. Untill I bought a CZ I would have sworn nothing could be more accurate.
I have a customized Marlin Squrrel that is a close second in accuracy. This gun got loads of testing and shot better than ANY rifle I could locate. again 3/4" groups @ 100yrds. (Picture below is from 50yrds.)
As of now, my CZ 452 with the LONG 29" barrel is hands down the most accurate 22LR I own. One benifit I REALLY like is the way it shoots CCI "CB LONG" bullets. They are all but silent!! If you shoot carefully (accurately at the head) they work wonderfully for garden raiding woodchucks!! I got one a couple years back, that was about 20#, and as big as a basketball in diameter.
Last weekend, I bought a new scope. So I swapped some scopes around and found that this gun will consistantly shoot three shot groups less than 1/2 MOA with a 3X9 AO Leupold scope. My gun really likes the RWS Rifle and CCI Subsonic rounds. When I am careful, shooting over sand bags front and back I can almost keep them touching at 100 yrds!
My vote is for the CZ 452 22LR rifle.
CW