Is the CO2 Crosman 600 22 caliber still considered better than average for its class?
The 600 is part of airgun history. Some need a rebuild, but there are at least couple of people out there that do that. If you have the original box and parts they go for over $400...otherwise around $180-$240.
Maybe try some wadcutters. JSB and H&N both make .22 cal wadcutters.