I've shot them in my Paramount, the 265 has outshot everything including the blue spaceship eld,, I've shot every sleek pitman,, Parker top bullet etc. Dennis at fury bullets built these bullets with a thinner jacket for blackhorn muzzleloader speeds,I'm sure they would work fine smokeless as long as the loads were not to hot,, as to the 250 and 275 and 300 grain start tips for my money there are the best purchase available in America, 4 hunting bullets they're the most accurate I have shot,, let me clarify I believe the sleek Pittman and Parker type bullets on the bench may out shoot the furys, but not by much,,for the money the furys are the best I have found, the 265 you mentioned is 453 instead of 452, Dennis design this to fit the diameter and bore of the Paramount rifle, however if you're sizing bullets it should work fine, get 50 of the star tip 250, and 50 of the 265 sit down and shoot you will become a believer