Using round ball ammo for the Haenel 28-R has been the norm. I then saw the original instructions on a old box and no, they are using diablo pellets. But pellets were shorter back then. I have tried vintage pellets with some luck but often they are not consistent, hard to find and expensive. Low and behold I tried the common Crosman Premier Wadcutters and yes it cycles perfectly. Cheap common answer how often does that work?