View Full Version : end shake and cylinder gap

June 26, 2009, 02:22 AM
A question. (Maybe should be put in the gunsmithing forum)? I watched a video by Larry Potterfield, from Midway. He shows how to get rid of excessive end shake in a S&W revolver. Correct me if wrong, but doesn't this do so by shimming the cylinder at the end of the yoke, thereby putting the cylinder always further back in the frame? In other words, keeping the cylinder/barrel gap opened up at maximum all the time? If I am correct, and have excessive cylinder/barrel clearance, isn't this is pointless?
P.S. I will post on a few other forums, too, for those that read others as well.

June 26, 2009, 08:57 PM
Yes it pushes the cylinder back where it should be.

The S&W end shake is limited by the end of the yoke barrel seating inside the rear of the cylinder.
End shake is when the yoke shaft gets battered shorter, and/or the inside of the cylinder gets impacted "deeper".
This allows the cylinder to move fore and aft in the frame.

Putting a washer inside the cylinder restores the length of the shaft and/or the inside rear of the cylinder to factory dimensions.
If the gun had too tight a barrel/cylinder gap to start with, repairing end shake will put it back too narrow.
If the gun had a too wide barrel/cylinder gap, it still will after the end shake is repaired.

In other words, repairing end shake will not cause excess barrel/cylinder gap. Barrel/cylinder gap is a moot point when the gun has end shake.
Barrel/cylinder gap is not really an issue since this is determined only in a gun that's in proper order and has no end shake.
When the gun has end shake, barrel/cylinder gap opens when the cylinder recoils to the rear and closes when the cylinder bounces off the rear of the frame and moves forward.

James K
June 26, 2009, 09:13 PM
Yep, removing the end shake will increase the barrel-cylinder gap. The gunsmith will make sure that nothing he does will increase the gap beyond specs. It is also possible to decrease the gap and the end shake by shimming the center of the extractor, but that will increase headspace. All those things are the result of wear, and guns, like any other mechanical device, do wear. Unless abuse is involved, the wear is normal, expected, and is no problem.

The fact is that a small amount of end shake is nothing to worry about, nor is the normal b/c gap or some rotational movement. Some folks are just perfectionists and want their guns to be absolutely perfect, something impossible to achieve except in some la-la land factory run by Santa's elves. They read about end shake, find it (and will find some in probably 90% of revolvers) and want it fixed, NOW! Then they read about rotational play, and want it fixed, NOW! Then they read about b/c gap and it has to be corrected NOW! And so on. Ego trip "A" folks who demand perfection are a PITA to a gunsmith (and any other service provider who comes in contact with them).

When wear becomes excessive, either due to use or abuse, the cylinder or barrel may have to be replaced; ultimately, the frame itself will become unrepairable and a new gun is needed. Most of our guns will never reach that point, but demonstration shooters go though many guns; the sponsor makes sure a continuous supply is available.


James K
June 26, 2009, 09:37 PM
I am going to make this a new post because of the disagreement here. While I was writing, Dfariswheel posted a different view that I would like to address.

From what I have observed over the years, end shake does not come from battering of the arbor and the inside of the cylinder but from battering of the ejector ratchet and the frame when the cylinder sets back. When a round is fired, the cartridge case, expanding from pressure, holds to the cylinder walls and pulls the cylinder back when it tries to move back under pressure. High pressure loads increase the condition both because the case is set back more forcefully and it grips the chamber wall more tightly; the result is greater cylinder battering, not of the arbor, but of the extractor and frame. Both that impact and the case impacting the frame will ultimately cause frame stretching, another condition that will result in end shake, but that is usually only after a lot of time and a lot of shooting.

You say the impact is on the arbor and the inside of the cylinder, but then you say the cylinder "bounces" off the frame; how could it do that without being battered itself and without battering the frame?

Shimming the arbor will certainly make up for that wear, but it will increase the b/c gap beyond what it was when the gun was new. Since factory spec b/g gap can run to .010" or more, some shimming will not result in an excess unless it was at the long end to begin with.


June 26, 2009, 10:06 PM
Both thoughtful replies from frequent posters, and more or less confirming what I thought.