High Standard Derringer 22 mag

[starnbar]

Got a HS 22 mag derringer with a broken firing pin got a new one put it back together and only the bottom chamber will fire it fires every time but the top chamber only gets a light mark on the rim any suggestions?

[Thin Man]

I have seen this before for either of 2 causes:
(1) The actuator spring is absent, or out of place during the assembly (they love to go on vacation during reassembly), or the actuator itself is out of it's seat in the frame. Take your pick on these. Or...
(2) Weak mainspring. Yes, this can be the result of a weak mainspring, one barrel will fire and the other (usually the top) will not. The mainspring will take a "set" from years of compression. "Stretching" your spring may restore it for a year at best, not reliable for long term. Numrick is out of these. I bought a few sections of steel (straight) brake line (each end flared with a nut inside the flare) but slightly different diameter tubes. Cut off the flares, then cut short lengths of tubing to "shim" your coil spring back to correct tension. (remove burrs inside & outside the shim) Test both tubes to find the diameter that will restrain the mainspring and still allow reassembly of the pistol (rather than having the side plate protruding). If you don't like steel tube, find small flat washers that will slip over the hammer strut and install them on the strut, grind off the opposite sides slightly to fit inside the frame. Or just buy 4-5 additional hammer strut washers (Numrich has these) to increase the tension of the hammer spring. Good luck with your project.