Dave, according to my research this should help you out. barrel length,24 inches, dia. at butt 1.21 ,dia at muzzle is .95, cal is .52,chamber is .60, length of chamber is 1.82, number of grooves is 6, width of grooves is .14, depth is .o1.This is what was reported from the navy yard by lt.Mitchell to capt. J.A. Dahlgren,in jan 1863, at this time capt was chief of ordnance.Let me know if this helps,and if you have any good drawing or pics of the breech and its workings I would appreciate it .Thanks Joe