We've been having some unpleasant weather here in SE PA recently. Hot, humid, and rainy with thunderstorms. However, yesterday I managed to sneak out for a couple hours to Boulder Valley Sportsmen's Association and shoot some targets on the woods walk course.
I took the Slotter-style plains rifle (which has become my favorite rifle) and aside from a capper full of CCI No.11s, a also brought along 6 of the homemade percussion caps from last month, in a 3D-printed star capper.
When shooting a caplock rifle it's always good to make sure the flash channel is clear before loading. This is most commonly done by popping a cap while holding the muzzle near a blade of grass or a leaf. If it moves you know the channel is clear.
Note that if I'm loading the rifle prior to a hunt, rather that popping a cap I'll use some rubbing alcohol and compressed air to ensure the channel is clear, especially since I may be loading (but not priming) the rifle at home. This is not a bad idea nowadays anyway, since No. 11 caps are hard to buy.
I did that with one of the homemade caps and it moved a blade of grass. However, when I loaded the rifle I found that the homebrew caps would not ignite the main charge unless I primed the nipple with 4Fg black powder first. That slowed the lock time down so that it was comparable with a flintlock.
(I keep a nipple primer in my shooting pouch in case I encounter ignition problems. This was the first time I actually needed it.)
Having tried them and found them wanting for use in sidelock rifles, I plan to make up another batch but add more priming compound.