The importance of endshake

Monday, January 15, 2007 Filed in: Revolvers, Gunsmithing
An often misunderstood aspect of revolver construction is the idea of endshake. Endshake is nothing more than the amount of back-and-forth movement (or front-to-back, if you prefer) that the cylinder is allowed to make.

Measuring endshake is easy: using a set of feeler gages, the cylinder is pushed forward and the barrel/cylinder gap is measured. Then, the cylinder is forced backward as far as it will go, and the gap measured again; the difference between the measurements is the endshake. (When making the second measurement, it is important to push the cylinder all the way back - even past any cylinder latch resistance.)

How much is acceptable? That varies depending on the gun; Colts are the most stringent, and need to have no more than .003" of endshake for "factory level" condition. A S&W is generally allowed a bit more leeway.

The amount of endshake any given gun will experience will vary a bit over the life of the gun. As the cylinder pushed backward by the force of the firing round, the ratchet (aka "ejector star") ultimately hits the rear of the frame opening, which stops the cylinder movement. With each round fired, the ratchet/star is slightly deformed, and the frame is very slightly stretched. Over a long period of time, this results in more space between the ratchet/star and the frame, which increases the endshake.

As the endshake increases, the amount of "free run" the cylinder has will increase the battering effect against the frame, resulting in even more wear - which increases the endshake, and the cycle repeats itself, getting progressively worse.

Why should endshake be a concern? Under the best of conditions, the revolver cylinder would have zero movement. Of course, that rarely happens in the real world; some endshake is inevitable. As endshake increases, though, several things happen: first, the impact on the frame, and frame stretching, increases; this can, in extreme cases, result in the frame becoming unsuitable for use.

The immediate effects can be more visible. In a Colt revolver, excessive endshake results in increased hand wear, which causes the timing to fail prematurely; in extreme cases, it can also cause bolt (the little "pop up" half-moon shaped piece in the bottom of the frame window) to wear to the point of replacement. In a Smith & Wesson (and to a slightly lesser extent Ruger), excess endshake manifests itself as an inconsistent trigger pull which gets worse as the endshake increases. These guns can also experience increased bolt wear, though not nearly to the degree of the more closely-fitted Colt.

(Interestingly, the Dan Wesson guns are very robust in terms of their endshake handing; the spring-loading bearing detent at the rear of the frame locates the cylinder at the forward-most position every time, and also serves to absorb a bit of the recoil force of the cylinder.)

An excessive amount of endshake can also affect accuracy. Not only does it change the relationship between the chamber and the forcing cone with every shot (and not necessarily consistently), but it also changes the barrel/cylinder gap; both can have a negative effect on the accuracy of the gun/load combination.

Setting the endshake to as close to zero as possible results in increased frame and ratchet/star life, better action quality in S&W guns, extended service intervals on Colts, and better accuracy on all guns. That's why it is one of the first things I check on any revolver that comes in to my shop!

-=[ Grant ]=-
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