Going from memory here, but my past readings suggested there is little if any velocity gain in 22LR's past about 18 inches. I think the longer barrels just offer a bit more weight, stability, and longer sight plain if one is doing irons.
I don't know how true it is, but I also heard that with the longer barrel you get more of a complete burn with a 22LR which translates into a minute accuracy advantage. Anshultz did a comprehensive test with .22LR's years ago, which I got a copy of (haven't got it anymore). They showed that with standard velocity .22LR ammunition, some barrels get maximum velocity at a shorter length and some at a longer length, with around 16 inches (from memory) being an average. With higher velocity .22LR, I would think that the optimum barrel length for velocity would be longer...perhaps 20 inches. However, optimum velocity is not necessarily the optimum length for accuracy in relation to the complete burn criteria (if it is valid). Another point when chopping Anshultz barrels, I had a heavy 23" which I got chopped to 22" (which is perfect for me). I asked the gunsmith where Anshultz puts the choke i.e. whether it is near the muzzle. I was told that the choke is NOT right at the end near the muzzle, and that an inch chopped would not take off the choke portion.
