Wish I could offer some help, but unfortunately the only help I can give is a "shade tree fix". I once owned an original Powell 16 ga. m/l S x S. The right lock mainspring was too weak to bust a cap. I couldn't find a replacement, and didn't know how to make one at the time, so I cut a piece of wood off of a wooden clothes pin, off the end of one of the "levers". I wedged it in the "V" of the spring tightly. It increased the strength and hammer fall velocity by more than enough to make it fire reliably, 100% of the time. I think I eventually found one close enough to replace it, with some redesigning, but that wedge worked for years, and never came out of place.
Not what you need to hear, I know, but maybe worth remembering in the future.
SRH
