Change the nipple to a musket nipple is all that is required, but I don't think it's required.

Frankly I've never needed a musket cap after tens ofthousands of shots

RWS Dynamit-Nobel #1075 caps. Exceptional performance.

Just keep the nipple clear with a nipple pick every few shots more or less depending on how fouling a powder your shooting.

Just curious but what powder are you shooting?

Tahquamenon