I also used CCI#11's with Pyrodex in my TC Hawkens years ago, and decided to experiment with musket caps.
But I found that the size of the hammer cup on a TC Hawken is barely large enough to come down over a musket cap, and if the hammer alignment is just slightly off, it would not strike evenly down on the cap, giving unreliable ignition worse than the normal #11 caps...I didn't want to get into bending hammers and all that, etc.
Then the CCI#11 magnums came out, I switched to them and never had a problem after that, so I abandoned the musket cap idea.