I sort of have been messing with FTF, etc. This is not going to be apples and apples even though I had similar problems with two recievers.
I have an older AJ 58 cal that I bought new. Threaded breech plug. I recently bought a 12 gauge barrel for it and it wouldn’t fire, with new CCI #11 caps, but about 1 out of 5 strikes. I could get caps to go off with a brass punch, hammer, gloves, and safety glasses 100% of the time. I put in a stronger hammer spring that I bought. Still a problem.
I bought a newer AJ receiver. Same problem. Took firing pin out and cleaned it. Still a problem. Never changed the hammer spring. I plan to change both to 209 primers if I can ever buy any. I got tired of all the cleanup just for testing so I changed the newer receiver over to a 12 gauge M48 barrel and started trying shotgun shells. Still nothing. I could see a slight print on the shotgun primers but no ignition. I pulled the firing pin on the newer receiver, put it in a lathe and made a shotgun pointed end - still nothing.
I pulled all the wood off of the old and new Huntsmen and ran them through a parts washer with mineral sprits. I got some loose stuff off but the mineral spirits didn’t seem to get the BP residue out of the two actions. I could still get a heavy black deposit when I used a rag in the corners.
Today I washed out the newer receiver with a spray can of brake cleaner. I got lots of black out and the rag came back clean afterwards. I rinsed the brake cleaner off the action parts and plastic trigger guard and did a bit of lubrication by flooding it with some, oily, mineral spirits. After the brake cleaner, mineral spirits rinse, and shotgun tip on the firing pin, the older receiver set off the shotgun shell first try and left a normal dent in the primer.
My plan is to convert both to the 209 primers with #60 O-rings to seal the BP from the action. If I can’t find the 209’s, I may also order the 25 ACP ignitions. I’ll use the brake cleaner, or something similar, to clean the receivers one last time. If I was going to keep using the #11 caps, I’d start cleaning the actions with brake cleaner on a regular basis. I wouldn’t want to drive out those pins to disassemble a Huntsman very often to scrub out all the action parts.
Right now I think the Huntsman action gets gummed up with BP residue and you can’t get it clean unless you disassemble it completely. Brake cleaner seems to clean up the residue.