I have a new englander sidelock in 54 cal.made by t/c never had to put powder in the nipple area to shoot.I think snapping a couple of caps before the main charge is drop is the way to go.
I snap 3 caps ,then run a clean patch in the barrel then use a well scraper with a clean patch .load the main charge and cap,I can say I never had a mis-fire.I also found a new nipple like hot shot work great and I use RWS 1075+ caps .