To answer the OP's question indirectly: The cap type seems to make little difference in my experience. E.g., one of my rifles has breech plugs and nipples for #10 and #11 percussion caps, musket caps, and shotshell primers. I've tried the first and the last extensively and have seen no difference in accuracy or where the projectile, usually a patched RB, impacts the target. Btw, since I have a surplus of #209 shotshell primers I tend to use them more often than the #10's and #11's.