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Old 07-10-2018, 10:57 PM
Sittinduck21 Sittinduck21 is offline
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Default Minimum Cylinder Gap

Hello, Gentlemen! I just bought a Model 19-3. I'm new to revolvers, and I was hoping you all could help me understand something. What is the minimum cylinder gap allowable on a Model 19 or any revolver for that matter? I did some googling, and the closest I came up with was 0.004" for GP100.

The gap on my revolver is barely visible. I couldn't find my feeler gauge, but I measured a piece of printer paper at 0.004" with my calipers and tried to slide it between the cylinder and the forcing cone. It didn't fit, not even a little.

What is the minimum gap between the cylinder and the forcing cone? Does the cylinder gap affect safety?
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Last edited by Sittinduck21; 07-10-2018 at 11:03 PM.
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Old 07-10-2018, 11:16 PM
ken158 ken158 is offline
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Generally - .004 to .010 is what you want. Less is better because it will grow as you shoot it.
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Old 07-10-2018, 11:20 PM
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I see .004 gap as perfect. To me a tight gap is better than a loose gap. I believe an acceptable tolerance is now .004 to .010. Used to be a smaller range between low ad high back in the day. As long as carbon buildup does not cause drag after shooting a few cylinders worth of rounds then you have no worries. Gunsmith can use shims to easily change gap but if yours is at .003 or .004 and you do not get dirt/carbon dragging on cylinder I would not change it. A bigger gap than .010 can cause accuracy and velocity issues. P.s. your picture looks perfect on your gun.

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Old 07-11-2018, 12:03 AM
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Jtown Jtown is offline
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I don't see anything wrong with the gap in your photo.

Walt
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Old 07-11-2018, 12:32 AM
Benchrest1 Benchrest1 is offline
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Looks fine too me.
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Old 07-11-2018, 07:22 AM
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Picture looks fine to me also. When inspecting a revolver for purchase I hold it up to light and look at that exact spot. If I see a just a sliver of light I am happy. To much bothers me way more.

The edge of a piece of paper may be harder to start than a steel feeler gauge, plus the calipers may well be compressing the paper a bit.
.004 is about as tight as I would like. But, lets say you had a revolver that measured .002 with cylinder pressed forward by hand, it would fire and function fine for a number of rounds and then any built up on cylinder and or barrel face would cause the cylinder to start dragging. With a real tight gap this could occur rapidly, depending on powder, bullet type, tolerance of cylinder to barrel alignment.

Great thing is a tight gap is easily fixed. Not so with a tight gap.
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Old 07-11-2018, 07:35 AM
44wheelman 44wheelman is offline
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Dan Wesson Supermags (357 max, 375, & 445) came with a .002” shim for setting the bbl gap. The .357 dw’s came with.006” shims.
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Old 07-11-2018, 08:06 AM
Green Frog Green Frog is offline
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If I could have a B-C gap of .003-.004" on all of my revolvers, I could probably do OK with that all my life. Much less and I'd worry that my casual cleaning habits might lead to some cylinder drag, but I wouldn't want to go very much more because of velocity loss and gas/lead spitting. If I am having a barrel installed, that's where I request that it be adjusted.

Froggie
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Old 07-11-2018, 10:34 AM
oddshooter oddshooter is offline
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If the cylinder spins evenly all the way around, I like a .002 b/c gap.
DW has definitely spoiled me. You set the gap where you want it when you screw in the barrel.

Less spitting and more velocity is usually a given with tighter gaps. Accuracy can also be better in that there is less time the bullet is in flight to the forcing cone and out of the cylinder (less wobble).


Look at your cylinder face. If it has rub marks at only one cylinder, then it is not spinning evenly and/or your gap is too tight. A new base pin or gap adjustment may be needed.

Clean your gun and don't use junk ammo. Build up of carbon shouldn't be a problem. I'd personally trade cleaning time for a tight b/c gap every day.

When the b/c gap hits above .006, I'm not a happy camper and I don't care what the factory thinks is within "specs".


Prescut

Last edited by oddshooter; 07-11-2018 at 10:38 AM.
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Old 07-11-2018, 11:26 AM
Toolguy Toolguy is online now
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Any time you have a tight gap, check for cylinder endshake. The center pin spring will push the center pin, which pushes on the bolt, which pushes the cylinder forward. I like to have a bit of front to back play on the thumblatch when the cylinder is closed so there is no pressure pushing the cylinder against the end of the crane. That makes it so the cylinder can turn more easily. It is one component of a good action job. This is done by filing some off the back end of the thumblatch where it comes to the end of the slot in the frame.

Sometimes the face of the cylinder is out of square, which leads to a variable gap as the cylinder rotates. This can be remedied by facing the cylinder on a lathe, but sometimes then requires the barrel to be set back to restore the correct gap.

In my experience, if the gun is carefully blueprinted so everything is as optimal as possible, you can get away with .002 gap for a while by shooting only jacketed bullets. Eventually some endshake will develop and will have to be reset. In more practical terms, .004 is about the minimum for jacketed only and .006 for lead or lead and jacketed. I don't like going over .006.
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Old 07-11-2018, 02:45 PM
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The critical question is, what's the rear gauge, or headspace? Check with feeler gauge between the rear of the cylinder and the breechface. In your case, the rear gauge should be .012" - .014".....tighter is better.
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Old 07-12-2018, 01:34 AM
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Years ago when I was in "Major Buying Mode" I'd carry a piece of .006" Feeler Gauge stock in my wallet for a "field check" of any Revolver I was interested in. Sometimes in my travels I just happened to stumble into a LGS - lol. For the most part any Revolver that was a loose goose with the .006 gauge I carried - I'd pass on. At that time .006" is what S&W considered about maximum and so did I. Today, S&W ships all kinds of tolerances and I believe they will accept anything under .012" (double the old spec).

As far as minimum B/C Gap goes, I think that anything less than .004" would be a lot of cleaning maintenance. You might get away with .003" but anything under that will more than likely bind up when dirty.
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Old 07-14-2018, 06:33 AM
Kframerbluvr Kframerbluvr is offline
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All of my Smiths measure about .004 except my ‘76 M10-5 which is .013.
I chronographed some loads through it and it read 75 FPS lower than my other 4” guns. That is how I discovered the excessive BCG. Will probably send it off to be corrected since it is the Bride’s current HD revolver.
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