I just went through something like that with my Blackhawk. The report from Ruger was a broken transfer bar. It took literally one week to send it to Ruger and get it home, that was west coast to east. It would take longer than that to order a part and fix it myself, if had the now how.

 

If the pin that holds the cylinder in place isn't all the way in, then the little spring on the end won't push the transfer bar back far enough to keep it from hitting the firing pin and it will lock up the action.

Here's a simple test.

Point the pistol straight up and try to cock it.

Gravity will make the transfer bar move back and clear the firing pin.

If you can cock it with the barrel pointed straight up then there's the problem. Look at the spring tip in that pin and make sure it's pushing the transfer bar back away from the firing pin.

 

I thought I might have a problem with my new Single Ten as it exhibited the same problem after I disassembled and reassembled it, After taking it apart and putting it back together again I soon realized I had not gotten my pin in properly the first time.