I would check to be absolutely certain, that your caps are fully seated on the tapered nipple. If not the hammer strike is cushioned and causes misfires. I know you stated your using #11 caps, but if you got #10 by mistake they are smaller and won't seat fully. On almost all my nipples, I put them in lathe and take a couple thousands off the tapered section, I get almost 100 % ignition now. I have also found caps are subject to absorbing moisture and spoiling, make sure caps are fresh. Also, when you dump your powder in, hold gun vertical and rap the reciever a few times to settle powder into breechplug. FFg can bridge across the breechplug opening and #11's don't throw much flame.