Have had a lot of .22 rifles over the years but I can say that the 452 American with the original 17" threaded barrel has been right on top as my favorite. It is very very accurate and not picky as to the ammo fed at all.
Since one is adding a can that will be in the area of 6" long, anything over the minimum legal length makes little sense. I did chronograph tests with several different types of ammo and there was little difference between a 17" American and a 21" Varmint...also tested was a 28" Ultra Lux and it was often slower than the other two.
17"/21"/28"
Federal Bulk: 1225/1227/1224
Remington Bulk: 1194/1230/1178
CCI Velocitor: 1364/1389/1351
Winchester PowerPoint: 1234/1267/1275
Remington Target: 1109/1093/1116
Winchester Super-X: 1187/1250/1193
CCI SGB: 1262/1272/1248
Remington Viper: 1355/1334/1316
CCI Stinger: 1554/1569/1551
Remington HS HP: 1233/1244/1229
CCI QuickShok: 1567/1556/1685
CCI MiniMag: 1278/1294/1240
Aguila Supermaximum: 1672/1688/1695
Aguila Subsonic: 999/998/970
CCI Subsonic: 1006/1001/967
Each round had a 5 shot group at 50 yards. Noted in my test was that the CCI MM and Aguila Subsonic gave the best groups of the day...
This is a target at 50 yards using a Tactical Solutions AXIOM Titanium suppressor and Winchester Super-X ammo. With the suppressor the rounds impact about .5" higher than w/o the suppressor. The bottom right target is 100 yards...
Started at the top left with 5 shots with the can and then top right without the can and then adjusted the scope.... As I shot I settled in and the groups got smaller.
Great gun....Bob