If you can get the cyl out, by getting the hammer down, do it.
Now see if the cyl stop (bolt) in the bottom of the frame cyl window doesn't go up and down when cocking the hammer. If not, disassemble grip and hammer only.
MY SHORTCUT FOR REMOVING JUST HAMMER and/or PAWL in New Models:
Recognize, when JUST NEEDING to remove the hammer and/or pawl, you do not need to hassle with the PESKY LOADING GATE SPRING pull the trigger pin, OR trigger/transfer bar.
Once you remove the grip frame, the hammer pin is the only other part you need to remove. After that, just pull the hammer back and all the way down, then depress the hammer plunger in the base of the hammer with a small tipped screwdriver to clear the trigger extension where the transfer bar connects to it. Let the hammer & pawl fall out. Reinstall the hammer and pawl back in the same way they came out. Push the plunger in by pushing it against the trigger extension just like you did with the tip of the small screwdriver, and the hammer will slip by the trigger extension. Piece o' cake.
Look for a stuck, bent, or broken plunger pin in the hammer base.
It's supposed to operate the cyl stop. If you take the grips off, you may be able to shake out a broken piece.
If that's the problem, call Ruger CS and they'll send you a new one free. Simple to replace.
Factory Video - New Model Ruger Disassembly:
http://www.youtube.com/watch?v=UfOXBa8K8Ow
Factory Video - NM Reassembly (shows hammer plunger assembly too):
http://www.youtube.com/watch?v=3zEKDqwkgEs&feature=related