I have a flintlock pistol that was "supposed to be" a .58 caliber, and the barrel is so marked. I had a horrible time loading that scudder with patched .570 round balls when I first got it, using the same .015-,017 patch material I used in my rifle. Had to rest the butt on the ground and hammer the loading rod down with a chunk of stove wood during one match. Finally I pulled the barrel and then the breech plug and miked it. Should have done that first instead of taking the word of whoever marked that dang barrel. It was a .560 bore, not a .580 ! I had been forcing an oversized round ball plus .030" of patching down it. Granted, it shot very accurately, perhaps because I was in effect swaging the bullet into the rifling. SO, my guess is that if you cannot seat your .490" round ball plus patching in that bore, either the bore is considerably less than .500 or the ball is bigger than you believe. Measure `em. My father often said, "Trust .... but verify. "