I have a High Standard Derringer, Model DM-101 Model in .22mag that does not reliably fire the upper chamber. From looking at the mechanism, it’s my opinion that the problem is in the design geometry of the internal parts. The firing pin (for want of a better term) alternates between the top and bottom chamber, and while the length is sufficient for a hard strike on the bottom, it is not quite long enough for the same strike protrusion distance on the top. My questions: 1) am I correct in the above assessment? And 2) is there a solution to fix the issue? There are much better modern pocket guns available, but I’m always tinkering on some old gun to return it to function.