I use electrical tape over the end of the barrel and over the area the cap is in. The reg's state that the cap can not be covered by an integral part of the riffle. I.E a manufactured piece attached to riffle. At least that's the way I read it, if I'm wrong oh well.
Ignition is to be wheel lock, matchlock,
flintlock, or percussion using original style
percussion caps that fit on the nipple and
are exposed to the weather. "Exposed to
the weather" means the percussion cap or
the frizzen must be visible and not capable
of being enclosed by an integral part of the
weapon proper. Primers designed to be
used in modern cartridges are not legal.