K. R. Bresien action

ive acquired an underhammer 12 gauge with a K. R. Bresien action. continue to get light strikes on the percussion cap. the second pull of the trigger sets it off every time. wondering if anybody has any experience with these actions and where a guy would begin if attempting to get a new trigger guard/hammer spring. picture is not my own but the exact setup that is on my firearm.

I had a chance to buy 2 beautiful slug guns built by Bresien owned by a lady who with her husband shot with him at Friendship. I was moving and so was she so I passed up on the deal even though it was pennies on the dollar. I tried to sell them for her through my friends in Arizona but there isn't any demand for them here. It's an Eastern thing I guess. This doesn't answer your question but I thought to pass it along. It's a slim chance but if anyone is interested in the slug guns I may be able to track them down.

The cap may be too small for the nipple. Did you try a different cap?

@lungbuster10, I don't have experience with that underhammer action, but I do have experience with caps that require two strikes to ignite.

Caps should be easy to ignite. Anytime some says that it takes two strikes of the cap to set it off, I want to take a look at the nipple. Is the tip mushroomed from a lot of strikes? A #11 nipple ought to be about 0.160" or slightly smaller in diameter for the cap to fit so the percussive compound is on the top of the nipple. Another plan for the recommendation of precision measuring devices. Spinning the nipple, after wrapping the threads in masking tape to protect the threads in an electric drill, and using a file to reduce the diameter at the tip may relieve the tip enough to fully seat the cap. Perhaps a replacement nipple is in order?