451 vs 454
Many salesmen don't know anything about BP guns.
Many older originals did use a 451 and is now mostly outdated information.
We have much better quality control than in antiquity.
Plus the big resellers get a better price break on 451 balls.
Best thing to do, is use a micrometer or ball gauge on your cylinder chamber.
Confirm the measurement.
If .446 to .448 then,451 would be ok.
But if .448 to .449 then better to use the 454.
wouldn't hurt to measure the barrel bore at the cylinder end, just to confirm.
Remember, once a ball is pressed into the cylinder it is no longer round.