Its 50 cal. Rayl bbl, 35 grs.3f goex 490 ball, .017 patch 2 and a half in group, just 6 in low For me this is a good group with my eyes and wobbly stance. I,ll be 69 next week and still enjoy all this very much. I think this will be the best pistol I ever built. Indiana deer legal. thanks L. Joe