Nice rifle - probably .43 Mauser. 370gr. A 1,360fps or so, black powder round - 77gr. black powder & 370gr. paper patched bullet. Brass is available and quite cheap made and stamped by Star Line. trackofthewolf.com sells it or used to. Lyman and RCBS made moulds. It is not for jacketed bullets as I don't think anyone makes them that size. .446" is normal for later than 1880 rifles in that chambering.