Barrel cylinder gap

Scooter1911 · Jan 7, 2018

I have not measured yet. Will possibly later today but the cylinder Gap on my 686 seems tight. Like .002-003. Will this have any negative effects? If so how do I correct?

Pisgah · Jan 7, 2018

Have you shot it? If not, do so and see if there's any negative effect. I know folks who'd mug you to get a revolver with a .002-.003 gap...

NYlakesider · Jan 7, 2018

If it functions well that gap will be fine! Most people with new guns are getting gaps on the bigger side. It appears that the tolerances are getting a little "relaxed" in that area!

OKFC05 · Jan 7, 2018

Also check end play. I've had people show me "too tight" that was really "too much end play" when I pushed the cylinder back with my hand.

cowboy4evr · Jan 7, 2018

The only problem I've ever had with a tight barrel to cylinder gap is when I got a little crud build up on the face of the cylinder it started binding up . Would have to stop and clean the face of the cylinder . Regards, Paul

oddshooter · Jan 7, 2018

Tight is great if the entire cylinder is like that and consistent. DON'T just measure one spot.

You must rotate the cylinder and measure many times.

If measurements are not consistent, cylinder may bind and start to take metal.

Tight is good. Less pressure lost out the gap.

Joe Hohmann · Jan 7, 2018

I have a 20 year-old 686. Last month I had a problem with 5 out of 250 .38 specials being out of spec. and being too tight. The cartridge rims were a tad too thick. Up to that batch (all bought in one transaction), no problems.

Scooter1911 · Jan 7, 2018

I might have put 50 rd through it w/o issue so far. If it starts to bind how do I correct it?

shottist · Jan 7, 2018

Happy problem

glenwolde · Jan 7, 2018

I had a derelict Model 66 I got at a gun show that I nursed back to life. After the yoke was stretched to remove the end shake the gap was so wide he turned the shoulder down and set the barrel back to a .003" gap.

I shoot lead bullet reloads and have tried many different powders and have never had a problem with it binding.

If it does bind, the simplest fix is to use a barrel facing tool. They are meant to square up the breech at the forcing cone but can be used to remove a bit of metal to open the gap up. But that's getting ahead of things.

The good news, I've put tens of thousands of rounds through the 66 and it's not showing any wear. Most have been .38's though.

chief38 · Jan 7, 2018

First shoot the gun and physically measure with a Feeler Gauge. Measure your End-shake also. If your End-shake exceeds .003" then you can correct it with Ron Power's shims and that in turn will also widen your Barrel Cylinder Gap. You will have solved two problems with one solution.

If your End-shake is not in excess, then you can either live with with the .002" -.003" and just clean the Cylinder face a little more than normal if it is sticking. You can also polish down the Forcing Cone .001" - .002" but this must be done carefully so that it does not become uneven and favor one side or the other. If you are not comfortable with doing so, then let a Professional GS do it. It's not a big job and should not cost much.

dfariswheel · Jan 7, 2018

Scooter1911 said:
I might have put 50 rd through it w/o issue so far. If it starts to bind how do I correct it?

If everything checks out, buy a "lead-away" type cloth at a gun store or order one from Brownell's.

This is a stiff cloth that wipes leading and carbon fouling off the front of the cylinder and rear of the barrel area.
Just rub the fouling and it comes right off.

WARNING: Don't use on a blued gun, it also wipes bluing right off.
I personally wouldn't use it on a nickel gun either.

Pay attention to the above references to "Cylinder end shake".
This is back and forth movement of the closed cylinder.

To measure......
Get a automotive feeler gage at Walmart or a auto store. These are cheap.
Push the cylinder to the rear and hold it there as you use the feeler gages to gage the gap between the cylinder face and the rear of the barrel.
Then push the cylinder forward and hold it there as you again gage the gap.

Subtract the one measurement from the other and that's how much end shake there is.
In the S&W you can have as much as about 0.006" before it needs repair.
If it's getting close, get it repaired. Once the end shake gets that bad the gun literally starts hammering and battering itself to death as the cylinder slams back and forth each time it's fired.

You can repair excessive end shake by buying some Power Co. stainless steel cylinder washers from Brownell's.
Grease the needed number of washers and drop into the cylinder shaft hole after disassembling the cylinder assembly.

NOTE: The measurement with the cylinder pushed to the rear is also the actual barrel-cylinder gap.
Gap usually should range from 0.004' to 0.008" with 0.005" being about perfect.
However, S&W now considers a gap of as much as 0.012" as being "in spec".

If your's is tighter that's okay AS LONG as it doesn't start binding from fouling buildup.
If the gun is a defense gun you may want to have the gap opened slightly to prevent a binding gun when you need it the most.
If it's just a fun gun, buy a lead-away cloth and clean the cylinder face and barrel area.

JayFramer · Jan 22, 2018

I seem to have the opposite problem! My two Model 64s that are otherwise in nice condition each have a .009" gap... bother!

dfariswheel · Jan 24, 2018

The S&W factory now says that gaps of 0.012" are in spec.
They say that a larger gap then the old specifications called for will only loose a small amount of feet per second velocity.

DWalt · Jan 24, 2018

You will be surprised at how large the effect of the barrel-cylinder gap is on MV. Small gaps are good.

Nevada Ed · Jan 24, 2018

Tight is a good thing...............

Loose and out of time can draw blood from your cheek !!

Kframerbluvr · Feb 10, 2018

DWalt said:
You will be surprised at how large the effect of the barrel-cylinder gap is on MV. Small gaps are good.

The difference between a .004 and .13 BCG in my 4” K frame .38s amounts to about 100 FPS with a 158 grain +P LHP.
Found this out when I bought a chronograph and checked my defense ammo through several different revolvers,

Protocall_Design · Feb 10, 2018

Kframerbluvr said:
The difference between a .004 and .13 BCG in my 4” K frame .38s amounts to about 100 FPS with a 158 grain +P LHP.
Found this out when I bought a chronograph and checked my defense ammo through several different revolvers,

I'm surprised that you would even shoot a gun with over 1/8" barrel to cylinder gap. I would think that much would lose a lot more pressure.

BLUEDOT37 · Feb 11, 2018

Toolguy said:
I'm surprised that you would even shoot a gun with over 1/8" barrel to cylinder gap. I would think that much would lose a lot more pressure.

Let's hope he meant .013", not .13"

.

joe44va · Feb 11, 2018

My last two 686+ purchases had gaps of 0.004 and 0.005 inches. Both 686-6. One 3", one 5". The barrel ends, however, are a bit rough.

Barrel cylinder gap

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