Thanx, I have it all apart and will check throughly. I would think cocked is cocked, but ...
Will also polish a bit more ... the inside of the Ruger leaves a bit to be desired compared to a BRN or Winc. Remove some 'drag'. The firing pin seems to extend plenty far into the chamber area when pushed by hand and nothing seems to blocking its movement so you might think firing pin spring. I will switch upper and lower as a trial. The upper hammer is longer and will have a different fall motion/pattern so a slightly weakened spring should not interfere with the upper bbl firing as much (my engineer brain sez!?). If it does then I have isolated the problem.
I still think firing pin and see that the hammer end of the lower pin is a bit more beat up. Ruger gives these pins different part numbers but the diffrence is not obvious to the Mk1 eyeball. No, I will not switch them.
I have trap guns with as many rounds through them as your Ruger but my Ruger would be [only] about half that as I had 3200s/101s/1100s/Citori's ... that I used lot at skeet, too. Says somehting good for the durability of all these great firearms!