Mechanical and Safety Inspection of the Double-Action Revolver Rev. 5Mar2021
Few shooters today understand the mechanics of double-action revolvers or how to conduct a mechanical and safety inspection. This article attempts to cover most aspects of annual service revolver inspection as practiced by police armorers back when your life depended upon your duty wheel gun going "bang~!" every time.
Dave Reiss wrote an excellent article on basic tune-up of the S&W revolver, published in The Fouling Shot Issue No.246 page 18. Here I've attempted to reconcile differences between what I was taught at Ruger, from Dave’s article which was specific to the S&W. Thanks also to Mike Wood of Police One who provided updated information regarding current model Ruger revolvers which came into common civilian carry use after I left the company. So, pay attention, Grasshopper and you’ll probably be more knowledgeable than anyone under age 70 working behind the gun shop counter today.
Open the cylinder, keeping the muzzle pointed in a safe direction. Provide a 5-gallon bucket of sand in the shop to use as a clearing barrel.
Confirm that all cylinder charge holes are empty and that the bore is clear.
On guns having adjustable rear sights, inspect for damage, a simple visual confirmation to make sure they’re not bent or damaged, and that screws are tight and not buggered.
Confirm proper function of the thumbpiece when releasing and opening the cylinder. S&Ws push forward, Colts pull backward, Ruger pushes inward.
Open and close the cylinder on each chamber, to ensure the ejector rod is not sticky on any of chamber due to burring of the tip of the ejector rod and subsequent drag on the forward locking bolt.
If the yoke/crane doesn’t pivot freely, in opening and closure, inspect the race for the yoke/crane screw for galling or rub marks, indicating the screw is a trifle long and should carefully shortened before installing and tightening again.
With the cylinder open, spin the cylinder and watch the end of the ejector rod for wobble.
Check with the fingers that ejector rod is tight, and not loose on threads. The threads in S&W ejector rods are fairly coarse, so taking the cylinder apart almost always requires re-adjustment to minimize run-out. Fixing run-out to the minimum does more for a smooth DA trigger pull than any spring work.
Verify that the ejector rod functions correctly at its full stroke and returns positively.
When ejector is held in its full rearward stroke examine the underside of the extractor and contact area of the cylinder for unburned propellant residue. If a revolver is used in sandy areas, sand may indeed collect in there as well. Brush clean if any is found present. Also inspect the small extractor alignment pins pressed into the cylinder, to ensure they’re not bent/broken/missing.
Inspect the firing pin hole in the recoil plate/frame bushing for peening or burrs. Gunsmith or armorer needs to stone off any burrs around firing pin hole and to re-seat and re-stake or replace the recoil plate or firing pin bushing if loose, cracked, damaged. Brownell’s sells the correct tool for doing this.
Press on the center pin which protrudes at the center of the extractor of an S&W or Ruger at rear of cylinder, to verify free center pin movement and positive return. Visually inspect the front end of the S&W center pin for peening. Stone off any burrs.
Close the cylinder, grasping it with thumb and forefinger. The cylinder must not strike the barrel when closed! This may be caused by the yoke/crane screw being damaged/worn/loose, or the gun having been shot loose by firing too many heavy loads, producing excessive cylinder end shake, or in a gun having been mis-assembled with a cylinder/yoke assembly from another gun [common with ex-foreign police imports now on the surplus market].
Confirm that both front and rear of the center pin on S&W or older Ruger Six series lock positive fore & aft as the cylinder is closed. Inspect crane lock function lock on later Ruger DAs.
Visually inspect fit of yoke/ crane at front of frame for gaps, which could indicate misalignment.
Perform the 4-way cylinder stop function check. With cylinder open hold the revolver in your firing hand. Pull back the thumb piece and hold it to the rear. On the Ruger GP/SP rock the cylinder release forward and hold. Or on the Kimber/Ruger LCR use a punch to push the tip of cylinder locking piece back into the frame and hold.
Pull the trigger double action and watch the cylinder stop, it should drop below the frame top surface and pop back up, slowly release the trigger and the stop should move forward towards the muzzle and the back to the rear. Down, up, forward and back. Visually check bolt or cylinder stop function at every charge hole and finger-wiggle cylinder for side-wobble at each charge hole.
Check SA timing, making sure that the revolver is unloaded. Insert three empties with an empty chamber between empty cases or dummies. Cock each chamber SLOWLY in SA with the weight of gun resting in the palm of hand for drag. Note any failure to "carry up" and for bolt or cylinder stop to engage locking bolt notches prior to full cock.
Check hammer for push-off from the full cock position.
Drop hammer, hold trigger back and check cylinder for wobble both sideways and fore & aft
With hammer down and trigger held back again check cylinder wobble, observe hammer nose driven protrusion and retraction below flush with recoil plate as trigger allowed to rebound forward.
Check DA indexing, closing the cylinder and slowly pulling the trigger through double action. The cylinder stop should pop up into the stop notch and have a slight resistance after it is in the notch as the trigger is pulled to the rear before the hammer falls. This carry-up test needs to be done slowly, as a rapid pull can mask a “DCU” (factory term for doesn’t carry up) problem.
With the empties still in the cylinder and the revolver still un-loaded, pulling the revolver action through vigorously DA while watching for positive trigger return and positive lockup of cylinder stop/bolt at each charge hole, before the hammer drops. Note any failure to "carry-up," or any "throw-by" i.e. over-rotation of the cylinder failing to lock up and rotating past a chamber, or sideways wobble.
Make sure the bolt or cylinder stop engages each locking notch the cylinder in place before the hammer falls. If locking skips on any cylinder then the cylinder stop and its spring needs to be replaced and a new cylinder stop fitted.
Throw-by test should always be done by a rapid DA pull; because many times an empty cylinder lacks the rotational momentum of a much heavier full cylinder and will not show a throw-by unless the trigger is pulled quite rapidly.
Check barrel-cylinder gap with feeler gage inserted completely through the frame opening between cylinder and barrel.
PASS is the dimension when a feeler gage is protruding out both sides of frame window between barrel and cylinder, which does not impair a complete rotation of the cylinder by pulling trigger through DA six times.
Minimum PASS dimension is 0.003", because a tighter barrel-cylinder gap may bind the cylinder when a gun gets hot or if shooting "dirty" ammo, such as black powder or lead bullets which are too hard, undersized and inadequately lubricated...
HOLD is the dimension when the feeler gage is protruding out both sides of the frame window between the barrel and cylinder, binding rotation so resistance is felt in a DA trigger squeeze.
Maximum hold dimension is 0.008" on a new gun when measured with "rear gage" or fired brass in cylinder.
Customer service maximum is 0.009" after correction of any felt cylinder end play.
At 0.010" cylinder gap the usual factory repair procedure is to fit a new “plus” [0.005" longer] cylinder. The usual gunsmith method is to set the barrel back a thread and refit after removing end shake, stretching the crane arbor on S&W or Ruger if necessary, or swaging a Colt cylinder bushing.
In pre-WW1 revolvers built for black powder ammunition barrel-cylinder gaps of up to 0.015” may be encountered. Guns having a gap over about 0.012” probably should not be fired without being repaired, because they are much more prone to “spitting” and “bullet-in-bore” malfunctions.
Check cylinder fore & aft for longitudinal movement. On Colts this check should be made with the trigger held to the rear in the fired mode, then cylinder lockup should then be rock-solid.
End shake is measured comparing the HOLD dimension measured twice, with and without empty brass or "GO" headspace gages in the chambers, or alternately with a 0.059" blade gage inserted between rear of cylinder and recoil plate. You can buy the blade gage from Brownells, and if you know what to look for they can be found as military surplus. The British used the same type of gage on the Victory Model S&Ws during WW2.
The least cylinder movement most people can “feel” is about 0.002.” If an S&W or Ruger and the cylinder "feels solid" with empty brass in the chambers, the gun is OK.
Colt maximum end play is 0.003, so if there is ANY felt end shake the gun is out of spec.
Measure the difference between "pass" cylinder gap dimension taken twice with and without brass in cylinder.
If there is any sideways cylinder wobble or hesitation of center pin to lock fore and aft, disassemble cylinder from the yoke, check crane or yoke alignment with gage and correct. [The Power Custom revolver jig is the best tool I’ve used for adjusting ejector rod run-out.]
Visually inspect locking bolt notches of cylinder for peening, particularly caused by cylinder backspin in S&Ws from heavy loads, such as +P in J-frame guns or +P+ in K-frame!
Visually inspect the barrel forcing cone for cracks. S&W 357 K frame barrels were likely to crack in the 6:00 region, where the barrel flat was milled to clear the cylinder gas ring, after about 3000 full charge .357 rounds. Barrel then requires replacement.
Inspect the frame window adjacent to the barrel extension for flame cutting and around the firing pin bushing for set-back or peening. These conditions are most likely to occur in light alloy frame off-duty guns if used excessively with +P ammunition. On S&W Scandium models having a pressed steel insert adjacent the barrel extension ensure that the insert is tight. Brush clean all crevices inside the frame window and use a bright flashlight and loupe to inspect light alloy frames for cracks.
"Tightening up" a revolver action to adjust timing/indexing may be as simple as peening a Colt hand a bit longer so that a charge hole which is "slow" carries up.
Factory procedure to correct DCU on S&W is to replace the hand with a slightly wider one, so its top comes closer to the inside of the hand slot. Thicker hands are sold for just that purpose. A factory K-frame hand is 0.091-0.095” thick, measured just below the hook. Most often a replacement hand 0.001-0.002” wider will correct the problem. Power Custom makes wider hands up to 0.105,” which require gunsmith fitting.
A gunsmith method to correct timing on older guns, particularly Colts, for which parts may not be available, is to bend the hand slightly. Rotate the hand medially toward cylinder centerline to speed up timing. Conversely to delay it. Sometimes the frame window needs to be opened just a wee bit to get timing correct. Brownell’s sells an offset file that makes this job much easier and precise. If that doesn’t solve the problem it’s probably because the ratchet cam surfaces have worn below the level of the hand slot and must either be replaced, or welded up, machined, recut, and heat-treated, by a gunsmith who is a great mechanic.
S&W and Ruger timing adjustments should always be made AFTER correcting end shake and squaring the end of the cylinder yoke or crane arbor. On S&Ws the end of the yoke is frequently out of square with the axis of cylinder rotation. Again, Brownells provides a nice tool for K, L, and N frames. For J frame, I improvise with a muzzle squaring tool.
A wobbly cylinder is usually caused by worn locking bolt notches and is usually corrected by fitting a new cylinder stop or bolt and sometimes may be corrected by skillful peening the locking bolt notches in the cylinder to reduce side play. In severe cases replacing the cylinder may be necessary, particularly on abused older Colts.
Reducing cylinder end play of a Ruger or S&W involves stretching the crane arbor or barrel to hold the cylinder back. Supporting the inside of the crane arbor is important when stretching to prevent collapse during the procedure. Stretching the crane also increases cylinder gap, which if it then becomes over 0.008" then requires either refitting a "long" cylinder, or setting the barrel back a thread and resetting the gap to factory specs. Above not applicable to Colts; the gas ring, which is integral to the cylinder, must be swaged to lengthen. In extreme cases, it is machined off and a bearing ring fabricated to take its place.
A “light technical inspection” or LTI, which consists of a detail strip, clean, inspect, tweak, and reassemble, not requiring fitting any replacement parts generally runs about $100 today.
A duty refurb which includes any machine work needed to straighten a bent frame (caused by using the gun as an impact weapon against a hard-headed subject), or setting the barrel back and refit to correct lose cylinder gap over 0.008", realigning the crane, correcting end shake, adjusting timing to correct a DCU (doesn't carry up) condition, replacing worn springs, targeting and adjusting point of impact on fixed sight revolvers, measuring hammer throw and striker indent using the government gage with copper crusher, and usually runs about $300 plus parts.
If your revolver duty refurb also requires a heavy duty cleaning, such as ultrasonic cleaning followed by a hot acid pickle to remove active rust, as may be necessitated by prolonged sweat or saltwater immersion, alternately hand carding off any internal rust, then replacing and fitting either a new cylinder, or barrel or critical internal parts and re-bluing, the bill can easily run $500-600 plus parts if done by a Pistolsmith Guild smith of established national reputation. If you really like the gun and will carry it for EDC, such work skillfully done is worth every penny!
Today you rarely find gunsmiths who actually MEASURE striker indent on carry guns! That's because while you can buy the gage holders and their drawings are in the public domain, the "C" size .225x.400" annealed coppers are provided only to the government and their contractors and cost $2 apiece in minimum lots of 500, the last time I bought any.
So civilian and PD gunsmiths who inspect and repair serious carry revolvers for a living developed a "work-around."
For checking hammer fall, an expedient screening check before test firing with duty ammo, to be done only after all mechanical corrections to action have been completed, is to loop a string around the hammer so that you can attach a trigger pull scale. Pull the trigger to start the hammer moving. Pause midway. Attach trigger pull gauge. Pull hammer back note weight just before it locks into single action. You want 50+ ounces for reliability. Balance between the hammer spring and trigger return spring are important.
Check driven protrusion of the hammer nose or frame-mounted firing pin, any pitting or damage to tip, replace any weak or modified springs.
A light trigger return spring and heavy hammer spring is a recipe for mechanical lockup in the action! Check for this during the cylinder timing check. Trigger return should not be sluggish. If so, it indicates that action springs are imbalanced and trigger return spring likely needs replacement!
Most important on an S&W is that the strain screw in the front of the grip frame is tight, and that the screw has not been shortened by Bubba to lighten his trigger pull! On a carry gun that light action can get you killed, because it may cause misfires. All .357 Mag. and most +P defense loads today use heavier-cupped primers to prevent the primer cup from flowing into the clearance around the hammer nose in the recoil plate. This would cause hard cylinder rotation.
Off-center firing pin indents which are off by more than ½ the diameter of the striker point are cause for concern. Over-rotation of the barrel causing thread choke and point of impact not in alignment with the sights is another. These are the sort of things that happen when people on the shop floor aren't paying attention, which you seldom read about in news stand gun rags. You have to have “been there.”
I have not discussed proper use of a "range rod" or correction of "thread choke" here, because most hobby shooters won't have the tools to properly assess or fix what they find and it is possible to damage the gun if you don't use them properly.
The barrel forcing cone compensates for slight misalignment of the chambers and bore. If bore-chamber alignment is WAY off, the gun will shave lead, especially from wadcutter bullets, which is annoying for the fellow standing next to you!
If you don’t have a “range rod,” a "spitting" test you can conduct yourself is to load the gun with factory .38 Special wadcutters, poke it inside a brown paper grocery bag, or cereal box and trigger off a cylinder full DA. Check the bag or box for holes or lead particles sticking in it!
Heavier cup primers are less sensitive, and more prone to misfires if you have a gun with lighter after-market springs to reduce DA trigger pull, inexpertly converted to DAO with shorter hammer-throw, or a bobbed hammer.
If unable to measure striker energy (minimum 0.010" Cu indent in DA on the size "C" copper in the gov't gage) test fire a full box of 50 rounds of your carry ammo in DA.
Accept if ZERO misfires, Retest if "1" misfire, reject outright if "2". If firing a second sample of 50 rounds runs OK, the gun is OK, but understand it is only 99%... If you get 2 misfires in 100 rounds don't carry the gun until you change ammo and re-test or repair it.
If your gunsmith asks for a full box of your expensive carry ammo to function test your gun, THAT is a good thing. If he can actually show you the gage holders, his $1000 box of coppers and explain their proper use, this means that you have an APG or FLETC certified revolver inspector who was probably trained at the S&W, Colt or Ruger factory especially for the Feds. THAT guy is absolutely "golden" and you absolutely should gently rub his bald head for good luck as if it were the Buddha's belly!
DA revolver manufacture has changed a lot since my time as an industrial engineer and QA manager in the industry. Today most manufacturers are making guns only for the civilian mass CCW market. The pressure is on production and profits, not quality. I'll every time spend more money for an old gun that works, having it rebuilt by a factory-trained police gunsmith who carried one and retired from the job, than for a new gee whiz mall ninja blaster assembled from a box of plastic parts. OK, I’m a dinosaur.
SO there you go, you now probably know more about old cop revolvers than any guy under age 70 who stands behind the counter at your local gun shop. So, you can assess when he is full of manure or not.