And sweeping both hammers back with your thumb? What happens in the middle of a flush and your thumb slips slightly, sweat or whatever, and one hammer doesn't go all the way back to the full cock notch and starts heading back in the opposite direction?
I knew the answer but I just checked to verify - if the hammer slips before full-cock it stops at half-cock - no problem. If your finger isn't on the trigger there is no problem.
And by the way, I have over 5,000 rounds through this 1866 non-rebounder without a single issue.
My Pieper 24 gauge with rebounding hammers is the same - if your finger is not on the trigger the hammer stops in the rebound position without hitting the firing pin.
Even in 1866 they had the technology right and in the 1940's they hadn't forgotten it.