[Gbro]

I hear(read) you all the way, however the wad in the musket cap is effectively blocking the orifice and in doing so is preventing the introduction of the heat.
Now on further testing i touched a lit match to the paper wad, and it was gone instantly. It must be treated with nitrite to facilitate combustion. But under the cap when its in place on the gun, the wad isn't fully burned. it is just charred and i have had to flick them off, and out of the nipple.
Now i might have some bad caps as i have had them in the tin, but for 5-6 years. My next test will be with new caps and i will install a 11 nipple also.
Now take the 209 shot shell primmer that is used on some imatation muzzel loaders. That primer will propel a retreaver dummy a long way. I once put a shot shell wad(no powder) through the celing tiles of the garage during a preplan for a trigger lock demmo. (i scrapped that part of the demmo, pronto)

I use the Flintlock ignition for the most part but also have the 2 guns w/ musket caps.
Many years ago i was in a class on muzzle loading and the instructor used percussion guns. He said that prior to loading it was prudent to snap a cap with a patch in the end of the muzzle or very close to a dry leaf to ensure a clean fire channel. The musket cap wasn't as available then and guns used #11 caps. I had the old Yankee rifle and no caps. Now i have caps and i feel they are not up to the performance of the originals. (just MHO)