I own a snub nosed SW 19-3 with 2,5" barrel, round butt, purchased mint from a collector some 25 years ago.  

I put an old pair of pachmayr rubber grips on it, I  find them more comfortable while firing, because hogues (rosewood and bantams) left the backstrap exposed.

I have a question about the gap between cylinder and barrel.
The gap is .006"  (0,15mm), the same left and right, on each one of the six chambers.
It has no end-shake at all.

Should I reduce the gap?
With a shimming kit?

Would a shimming kit increase the free-bore? The firing pin is attached to the hammer as you know, and I have had some striking issues with reloading primers (mostly CCI brand, harder I guess). The hammer spring is already set "hard".

I fired several thousands rounds in it, mostly reloads, 99% of them in double-action. The timing is still correct, but in the future I know I will have to replace and fit the "hand" to ensure the cylinder stop to act before the hammer falls.

Sometimes I noticed the projection of small particles from the gap, I guess maybe the reload were a bit hot, but not that hot. That's why I'm a bit concerned about the gap.

Thank you.

That gap is fine

Nice gun

.006 is a Good split between reliability and pressure loss from excessive gap.

Nice revolver!

.006 is well within the acceptable range.

Thanks... I have been looking around to find it for a while, because I like best this blued one instead of the ss model 66. I like SW because I can fire it with a two-stage pull double action, firing is fast and accurate.

Thank you
I was a bit concerned about that, mostly because of those particles projected from the gap. But now I assume I must research the cause elsewhere... In the reloads I guess.

OP, you have a super fine revolver.  I have two of the same model but nickel plated.  I have not measured the gap on mine but .006 is fine.  The particle ejection (spitting) you get is a product of unburned propellant and/or particles of lead from cast or swaged bullets.  It is not unusual with revolvers.  I have a Model 27 that spits on one chamber and have no idea why as the timing is spot on.  Modifying the forcing cone might stop it but is not worth the effort in my opinion.  Good shooting to you ; it will be a long time before the timing on your revolver will need any adjustment.

congrats, nice gun!

might be my imagination but I find(in general) blued(or nickel) guns have smoother actions than stainless.

I have a pair of 19-3 snubbies that had their hammers bobbed and some action work, they are fast guns in DA and can(if your careful) fire single action and are easy to stack the triggers if wanted.

snub nose smiths are my favorite guns.

Uncoated lead bullets? I had a new Colt Police Positive around 1980 that would spit lead. I never knew if it was a timing issue or the forcing cone that caused it. A really good cleaning won't hurt any firearm.  

Cylinder gaps are supposed to be around .005" from the factory, I think yours is very close to new. Consider trying faster burning powders and lighter loads when using lead. Some powders create a lot more muzzle flash and blast than wanted, using them with lead bullets causes leading and even front strap erosion with full power jacketed bullets.

I loaded up some 135 grain Speer short barrel bullets in .357 Magnum using 8.5 grains of Power Pistol. It's supposed to duplicate Speer's low recoil .357 self-defense load. The blast wave could clearly be seen exiting the cylinder gap all 360 degrees. The fireball was impressive as well. IMO this isn't good for you or your gun. I owned a .41 Magnum with a 3" barrel and it developed rather severe frame strap erosion over time with me never loading any full power loads for it.

Some people really enjoy shooting maximum loads from magnum revolvers and more power to them. I simply refuse to do it any more. I load the majority of my magnum revolvers on the low end of load data. A 158 grain SWC traveling at 950 to 1000 fps from a .357 is plenty, even for self-defense. It's easy on the brass, the firearm and me. It allows for very quick follow up shots.

You could easily get there with .38sp brass btw. That way the shorter throw of the ejector rod would be less of an issue.

.006 is just fine for a gap.
Have you scoped each cylinder to check timing / alignment? Might explain the particulate if one or more is slightly out… but as mentioned, it’s likely just unburnt powder and residues.

Exactly what I was going to suggest as well.

Yes I checked the chambers and the gap is the same on each one. I am pretty sure by now that the particles were just due to unburned powder. The reloads were 142grs jacketed but the rather slow rate burning powder and the short barrel did the rest. I think I'm no longer concerned about the gap

We're referring to the carry up/timing and barrel/cylinder alignment... not the gap.

In other words, you need to make sure that the hand is rotating the cylinder fully into position so each chamber is properly aligned with the barrel and the cylinder stop is engaging each cylinder locking notch before the hammer drops.

The following link (hoping this doesn't violate any forum rules) provides some very detailed/helpful descriptions and instructions:

http://smith-wessonforum.com/s-w-smithing/527760-faq.html

Yes, the timing Is right and so is the alignment. The cylinder stop does its job very nicely.
Thanks for the hint

If the timing and alignment are good... and the gap is what most would consider ideal, then you should be GTG.