The 54 cal pellets measure .497 and fit very nicely in a .500 barrel I have used them for years as part of the procedure of finding a load. DO NOT use them if it takes your barrel over the recommended grain amount; check your manuel for that. I have one of the old type 54 cal. rengade TC hawkens that shoots them better than any thing else with a round ball.
I HAVE HESITATED TO COMMENT ON THIS BECAUSE TWO WILL TAKE THE 100 GR LIMIT BARRELS WAY OVER THE LIMIT.
TWO IS 120 GRAINS, AND THE LIMIT FOR MY OLDTCRENEGADE.
LEE