Caliber? LARGE, but nothing y'all haven't shot before. What is different mebbe is the amount of lead it chucks down range. If I recall correctly it uses an 800 grain bullet.
It belongs to one of the members here, maybe he'll chime in on the specifics.
A few days ago it fired a 30 shot string of 31.282"........at 200 yards. By the way, it has a home made scope as well. Don't confuse "home made" with amateur.