Single Six problem

I recently came by a single six made in 1975, and it is a one-owner (until now). It was shot very little, but definitely shows some care and surface rust issues. I think it could be called a "throw in the vehicle gun". When cocking, it hangs up at about half-cock. It does this with either cylinder, LR or Mag. Without a cylinder, it cocks fine. It may have been opened up at one time, but it had been a long time ago. The problem does not seem to be with the Base Pin Assembly. Could it be a pawl problem? Base Pin? Any recomendations? Thanks for any ideas.

I had a similar problem w/ a different revolver, but it turned out to be a worn hand. I'm by no means a gunsmith, but just thought I'd offer some input.

If it's a New Model, check to see if the transfer bar is hanging up on the firing pin instead of riding over it (you can also hold the barrel vertical and see if there's any difference in function). I bent mine away a little and then stoned a new bevel on the leading edge on the transfer bar.;)