Ruger NMV and blackpowder

[cal44walker]

   Was out this morning running some BP through my Ruger NMV's. One ran flawlessly for 50 rounds however the other one did 5 rounds and started binding. Got home a made a few measurements. I don't have a feeler gauge on me but I used a piece of paper measured at 0.07mm and checked cylinder gaps. The one that runs fine has a visibly larger gap of aproximatly 0.1 mm and the other one that gave me trouble can only just get a piece of paper in there. 0.07 mm is 0.003 inches ie the minimum of what one should set the gap to. If I pushed the cylinder against the barrel slightly then it closed all the way up and the paper was stuck and the cylinder would bind. I did some other checks and found the cylinder pin of the troublesome gun to be only 6.25mm in diameter as aposed to 6.31 of the other gun. From what I can see the cylinder gap is already minimum but combine that with the cylinder canting slightly on the base pin and the hand pushing forwards, then the cylinder gap closes to zero. Add in BP fouling and voila......binding cylinder.
  I've ordered 2 base pins from Belt Mountian that are 6.33mm in diameter to tighten the play in the cylinder and I'll have to either get a piloted tool from Brownells or get the barrel off and in the lathe to increase the haedspace to 0.008" - 0.010". I might also make a custom bushing and press that in to remove all cylinder endshake. While I'm busy woth that I'm also considering squaring up the area around the front of the frame just below the barrel where the base runs through. The guys at Ruger obviously did'nt think it needed to be sqaured up.......

[wildman1]

I use two NMV's with BP and they will do 6 stages with no problem. When I'm in a dry climate I will sometimes need a drop of water and Dawn dish soap on the front of the cyl. WM

[Coffinmaker]

That will be a lot of work for essentially no gain.  Step one with a Ruger is to check/correct the cylinder throats.  Recut the forcing cone to 11 degrees and correct barrel/cylinder gap.  Smokeless should be .006 +/- and for BP maybe a little more.  Anything else with a Ruger is waisted effort.  You can correct the barrel/cylinder gap with a sharp bastard file.
But .....
It's your gun.  Good luck

Coffinmaker