I have slain the deer and hogs with my muzzleloaders with Goex ffg and #11 caps. Never had a misfire.
Remember, #11 caps are what make cap and ball pistols go bang, many a man has bet his life on the reliability of these caps, and won.
Clean your rifle real well, clean all around the inside of the drum with pipe cleaners, get all the oil out, and you should have no problem with your #11 caps.