GP 100 Cylinder gap

[noquarter]

After the last range session, I noticed a lot of what I would call heat stains on the front 1/3 of the cylinder. Never had that happen before. The gun is a GP 100 SS 4" bbl .357. I bought it NIB in Dec, and it has had 500 - 800 rounds of .38 / .357 through it since then - all factory ammo, no reloads. Looking at the cylinder to bbl gap, it looks wider than I remember. I tried a .012 feeler gauge (smallest I had) and it wanted to go but wouldn't. I've always heard .003 - .006 as the preferred gap, with .008 the high limit. Is that correct?
2nd question - I know it would have to go to Ruger to be adjusted, but I am curious to know what sets the clearance? It wasn't obvious from the exploded view.
Oh, yeah - the SP101 has been eating the same ammo with no trouble.
Thanks.

 

[Jimbo357mag]

According to a reliable source the B/C gap for a GP should be between .004" - .008" with .006" being optimum. The cylinder end-shake should be .002" - .005". The end-shake is measured by pushing the cylinder forward and checking the B/C gap again. Subtract the second reading from the first to get the end-shake. The headspace, the distance between the recoil shield and a new case, is also very important. The headspace should be .008" - .012" with .010" as optimum. The cylinder can be adjusted with thin shims. Making any one adjustment can throw off the other adjustments.

Now to answer your questions. The powder stains on the cylinder are normal and can be cleaned off with powder solvent and a soft brush or with a 'lead-away' cloth if your gun is stainless steel. I believe overheating the stainless can cause permanent discoloration.

What sets the clearances of the cylinder is the ratchet riding on the frame in the back and in the front of the cylinder riding on the crane tube and how far the barrel is screwed in the front of the frame. :D

... Jimbo

 

[noquarter]

Thanks, Jimbo. Nice to know how they set it. I think the discoloration is a stain, not a real heat stain even though it looks like a heat stain. My concern was that it is going 1/2 way up the flutes after a box of .38, which it didn't do before. I will get a good gauge Mon and check the B/C gap, End shake feels good (again no gauge) - you can feel the movement but not see it.
Again, Thanks.