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STORY: Hamilton S. Bowen Fine-tuning the double-action revolver. sixGuN FLu M ost box-stock autoloaders will work pretty well right out of the box fired with the ball ammo most were designed to shoot. Where most go off the rails is with ammo they don’t like. Fed properly, and absent undue wear or abuse, they will soldier on forever. Double-action revolvers, on the other hand, will function with virtually anything that 1) has a live, properly seated primer, 2) fits in the chamber and 3) doesn’t seize in the chamber or blow the gun up on the first shot. But double-action revolvers, especially big bores, seem more prone to get out of kilter through ordinary use and may, occasionally, require some minor adjustments to remain healthy and happy. While these remarks are generally applicable to all DA revolvers, they are specifically tailored to the ubiquitous Smith & Wesson guns. There are three major problems that crop up. Typically, the symptoms are the same: the gun develops a ‘gallop’ or cramp in the action cycle that can vary from chamber-to-chamber. In combination, a couple of the problems can bring the cycle to a halt. Happily, the condition most responsible is the least troublesome to set aright. It is cylinder endfloat, defined as the back and forth movement of the cylinder on the “yoke” in S&W parlance (“crane” in others) along its center axis. In the extreme cases causing action binding, you can almost always hear a click when you move the cylinder back and forth. If you look across the barrel-to-cylinder gap, you can see it tighten and loosen when the action is cycled. If the hand tips the cylinder forward enough to drag on the barrel extension, you will often feel a noticeable increase in cycling pressure. It is not unheard of for the gun to simply stop running mid trigger stroke. The basic cause is usually just using the gun. The basic S&W design is over a 100 years old and did not contemplate magnum cartridges. The small yoke-to-cylinder bearing area simply batters in time and the increased clearance allows longitudinal cylinder movement. The basic fix it to take up the slack. This is done variously through yoke-stretching procedures or shims. I find the Power Custom shims more predictable. Using as many of the .002" shims as is necessary, I’ll put Getting the best performance from a high-quality revolver may require some fine tuning. Sorting out yoke fit requires a spot-facing cutter with its guide sleeve and a yoke alignment tool (above). The shims take up any slack. Yoke alignment is checked with this special gauge pin (below). The tip of the tool must enter the receiver center pinhole without hitching or binding. them in the bottom of the cylinder yoke bore where the yoke bears and try the cylinder. When it closes stiffly, I know we’re there. I use a Brownells/ Power Custom yoke-squaring tool to remove just enough material to let the cylinder run free with no back-andforth movement. A side benefit is an increased bearing surface once trued up. This should not materially change the headspace but you must check it to be sure. Feeler gauges will do for an open-back cylinder. A recessed head cylinder will require both feeler gauges and depth micrometer. The barrel-to-cylinder gap may show a small increase but usually it remains in spec. The next adjustment that may be necessary to cure a galloping action is yoke alignment. The cylinder center pin runs in a corresponding hole in the standing breech. If the yoke isn’t in exact alignment with this hole, the center pin will bear on just one side of pinhole and can cause dragging or binding problems, especially if the extractor isn’t well centered in the cylinder. Adjustment is pretty simple and requires a simple yoke alignment gauge and an adjusting tool. With the gun held firmly in a padded vise 20 W W W. G U N S M A G A Z I N E . C O M • O C T O B E R 2 0 1 2