Copy/Paste from danwesson forum dot com:
CRANE LOCK INSTALLED INCORRECTLY
Hi folks, I just spent an hour or two trying to work out how to put a shim into the 15/2 revolver to reduce the .010″ gap I had when the cylinder was pushed to the rear, overriding the ball / spring tension.
I was dismayed at the amount of movement forwards and backwards when I push / pulled the crane with the cylinder removed. Couldn't work out how to fix this – I thought the revolver was worn out and that I had wasted my $s.
Fortunately, the crane lock slipped out while I was wriggling the crane, and then IT came to me – I had the machined face of the crane lock pointing to the front of the revolver. If I turned the crane lock around, then the rounded side would face the front of the revolver, pulling the entire crane back towards the rear of the revolver. When I did this, the extra movement or slack in the crane all but disappeared. Felt like a completely different assembly. This also effectively moved the front of the cylinder back a few thousands of an inch.
I then reassembled the 15/2 and am pleased to say, I have a total gap of .005″ when I push the cylinder back as hard as I can towards the rear of the revolver. So the current settings are just under .002″ (firm fit) barrel to cylinder at rest, .005″ total gap when forcing the cylinder to the rear.
JUST BY TURNING THE CRANE LOCK SO THAT THE MACHINED SIDE FACES THE REAR OF THE REVOLVER HAS REMOVED .005″ OF FRONT TO BACK MOVEMENT.
This is also when the revolver is cold and hasn't fired a round.
Tomorrow I'll take it to the range and put a few hundred full loads through it to see what happens.
Unquote
IMO it could be the ball/detent sitting in the crane, the inside machined part that faces the revolver frame indent.
At home I could confirm by looking at my Model 44 with the crane/cylinder in the open position, but I'm two weeks away from that time/place. If this is it, you are also missing a spring and it's firm crimp. Should be an empty hole in there!?!?
PS: I looked at the on-line schematic as well, I think these details are missing from the Numrich parts diagram.
maybe?