"only" is a flag. He may have long loaded the cartridges, B 78 no need to cycle through a magazine, many single shots are loaded to suit the leade & too long for a lever action.

Marlins are strong, But I would not fire anybody else's re-loads. I would pull the bullets dump the powder and re load them my self. May want to use his 50 gr data. Hodgdons recommended are heavy recoilers.

Boats