Cylinder gap questions......

[MIL-DOT]

Apologies for asking what must have been covered, ad nauseum,already, but I couldn't dredge up up what I am looking for, here or on Google.
I have an old Smith 28, and am concerned about cylinder gap, and have read the various,progressively shifting ideals according to S&W ( from .002 -.010, depending ).
Anyway,I'm wondering if I should check the gap with the cylinder as it sits normally, empty, or if I should pull the cylinder back towards the rear, and check that slightly larger gap. I think the front-back cylinder movement is miniscule and not a concern, but when talking thousandths of an inch, it is a factor, and I'm wondering which position is the proper place to measure cylinder gap.
Any help much appreciated......

 

[GP100man]

The cyl movement back & forth is end shake & directly affects cyl gap & headspace !

I personally like to see .006-008" cyl gap , endshake I don`t like to see anything over .005"

If the revolver falls within these numbers it`ll run "dirty" .

I had some colts that the cyl gap was so tite ya had to shoot full magnum loads to keep the end of the cyl blown clean , or stop & scrub the foulin off the cyl every 25 rnds.

 

[Walkalong]

I have a Model 28. The cylinder gap can be measured with a ruler. It shoots "slow", but very well. I have always measured the gap with the biggest feeler gauge that will enter the space under lock up. I do not know if that is the correct way to check it though.

 

[Onmilo]

It is correct to measure cylinder gap with the revolver at full cock lock up.
It should fall between .005" and .008" as previously noted.

Endshake is measure with the hammer at rest and the gap measurement is taken with the cylinder empty and pulled back to the recoil plate.
This gives you the maximum measurement which is then subtracted from the cylinder gap measurement to determine the amount of maximum endshake.

Headspace is checked with the cylinder loaded, preferably with action dummies, and the hammer at full cock.
Ideally, there should be no more than .002" gap clearance between cartridge head and recoil shield @ firing pin on all chambers.HTH

 

[texagun]

From the Inspection Guide For Smith & Wesson Revolvers:

"Barrel-to-cylinder gap: The ideal B/C gap is .006”. A close gap will cause the cylinder to drag when fouled from shooting residue. A wide gap will loose muzzle velocity and may spit particles. The normal usable range is from .004~.010”

Hold the cylinder to the rear and insert the thickest gap gauge that will fit between the cylinder face and the rear of the barrel (with friction). This will be the B/C gap.

Cylinder endshake: This test will measure the front to back free travel of the cylinder. It is a good indicator of wear from shooting. Anything over .002” is considered excessive.

Hold the cylinder forward and insert the thickest gap gauge that will fit between the cylinder face and the rear of the barrel with minimal friction. Subtract the measurement from the B/C gap. This will be the cylinder endshake."

 

[Mizar]

Cylinder endshake:... Anything over .002” is considered excessive.

According to Dfariswheel, the maximum endshake for S&W revolvers is 0.006" and 0.003" is the maximum for old style Colts.

Boris

 

[texagun]

Quote:
Cylinder endshake:... Anything over .002” is considered excessive.

According to Dfariswheel, the maximum endshake for S&W revolvers is 0.006"

Really no contradiction there. While the maximum for S&W revolvers is .006, anything over .002 can be considered excessive. These are generally accepted guidelines. Others will use other guidelines.

 

[MIL-DOT]

Many thanks for the replies,guys. I borrowed a gap tool from a mechanic freind the other day, and while pulling the cylinder to the rear, I was able to barely squeeze a .013 in there. "Walkalong" just said above that he could about check his model 28's gap with a ruler, yet it was still a good shooter, but for a bit of velocity loss. I traded a gun I had very little money in for this 28, and I don't expect to be putting lots of ammo through it, but am I OK here, or is there some kind of genuine safety issue I need to be concerned about?
I'm waiting to hear from a local smith who's getting ready to fire up his blueing tanks, but I don't want to put money into something that isn't mechanically sound ( though he and another local smith have looked at it and like the gun). And I especially don't want to have to send it off to S&W, when I could just ditch the gun at a gunshow, and use the money saved from a re-blueing and a factory gap job, to just buy another pistol. See what I mean ? Again, any insight much appreciated.....

 

[Walkalong]

I just measured mine and it is .015. As I posted, it shoots quite well, but it gives 4" tube like velocities. Whether that is the gap, the barrel, or both, I don't really know, but I have to believe the gap attributes to the low velocities.

Cases are dirtier out of it than other .357's with the same load signaling lower peak pressures, which I assume can be attributed to the gap as well.

 

[unspellable]

I ran some tests of cylinder gap effects with a couple of Dan Wessons with the adjustable gap. In the 44 Magnum with rather mild factory loads and a jacketed bullet the revolver began to spit rather badly when the gap reached 0.012 inch. The gap did not have as much effect on velocity as you would think.

 

[Ole Coot]

If you happen to trip over a revolver you want to check, full cock and a business card will give you a very accurate measurement.

 

[Walkalong]

the revolver began to spit rather badly

That is usually due to poor alignment. I have more than one revolver with big gaps, and they don't seem to spit crud.

 

[unspellable]

They don't come with better alignment than a Dan Wesson. You have to go to Freedom arms just to match the alignment. Line bored and all that. (Also checked for alignment, dead on.)

I don't think it was spitting metal, rather powder residue, but still unpleasant in the face.