K, L frames...not all things are equal.

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dahermit

New member
I shoot my four S&W double-actions for non-defensive double-action shooting exclusively. Over the years I have tuned them for the lightest possible double-action trigger pulls with Federal primers exclusively. My current trigger pulls (via a Burkley pull gauge) are as follows:

S&W 686------6 lbs.
S&W 66-------6 lbs.
S&W 696------6.5 lbs.
S&W 14 (K38)..8 lbs.

I have done pretty much the same to all those guns, Wolff Spring Kits (lightened main spring and lightened trigger return springs), smoothed mating double-action surfaces, shimmed any hammer and trigger misalignments, cut two coils off the cylinder release springs, painted the insides with layout dye to detect any metal to metal contact, etc.

However, not matter what I try, the K38 (circa 1959), will produce light strikes if I go any lower than the .012 shim I put between the strain screw and the grooved Wolff ribbed mainspring. No matter what I do, it will not reliably fire my Federal primers...which is counterintuitive inasmuch as the lock-work of the four guns are virtually identical.

The two pounds difference has to have something to do with the hammer fall, but I can find no evidence that the hammer nose (firing pin), or the hammer is making contact with the frame prior to firing, and thus requires more force. I have tried a different hammer and longer firing pin, but that made zero difference in whether or not the primers would fire.

In theory, I should be able to get the K38 as light as the other three. From those with the requisite experience with S&W double actions, what can be the possible difference? Any suggested "cure"?

Please, no responses like: "Why do you need a trigger pull that light anyway?" or, "I always just strengthen my fingers...", etc. Please stick to the question as asked.
 
Should be any shims or cutting springs in a proper trigger job. Polishing the parts and changing the springs only.
Which Wolff springs? They sell a swarm of 'em. Wolff rebound springs are available in 11, 12, 13, 14, 15, & 16 lb. ratings.
"...will not reliably fire my Federal primers..." They seated properly? Just a tick below flush and level with the case head. What's it do with other brands?
 
Should be any shims or cutting springs in a proper trigger job.
Polishing the parts and changing the springs only.
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Cutting two coils from the cylinder release spring is a standard procedure in lightening the double action pull as per at least one of the authorities on S&W revolvers.
Which Wolff springs? They sell a swarm of 'em. Wolff rebound springs are available in 11, 12, 13, 14, 15, & 16 lb. ratings.
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What difference does that make? The rebound spring has nothing to do with the force of the hammer fall.
"...will not reliably fire my Federal primers..." They seated properly? Just a tick below flush and level with the case head.
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No, I always make sure to seat them erratically. Come on now, if I was not seating them properly, don't you think it would show up in the other three guns?:rolleyes:
What's it do with other brands?
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It has nothing to do with the other brands inasmuch as I only use Federal because they are considered to be the most sensitive and I want as light of a trigger pull as possible.
You seemed to have missed the point completely and not kept to the subject of, what can be causing such a required heavier trigger pull in just one of the guns.
 
I've got one possibility for you. Measure the arc distance between the pivot point on your K38 hammer and the firing pin nose, then compare that to the arc distance on one of the others. If the K38 firing pin nose is traveling in a smaller arc then that is one explanation. I.E., a longer arc means the firing pin is traveling at a faster speed thus hitting the primer harder.
 
I've got one possibility for you. Measure the arc distance between the pivot point on your K38 hammer and the firing pin nose, then compare that to the arc distance on one of the others. If the K38 firing pin nose is traveling in a smaller arc then that is one explanation. I.E., a longer arc means the firing pin is traveling at a faster speed thus hitting the primer harder.
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Thanks, I will measure that and will see.
 
I've not measured the differences in the arc of the firing pin to pivot between the different models to know what the exact distances are, but that does come into play. There are changes between the frames in this.

You might want to check and make sure the firing pin is not loose in the hammer, and use a feeler gauge to measure the distance of the rear cylinder gap to the frame on that revolver too. All should have the same gap, within a couple thou. for the same cartridge. Last, you might need to check the firing pin protrusion.

I never cut springs, but take down the OD on them with a belt sander, so they lose some of their tension. The rebound slide spring and the cylinder stop spring would not cause the hammer to strike any less harder. That is all in the hammer spring, and what I mentioned above.

A fine stoned sear surface will help, of course, as well as the fit and finish of the hammer stud, and the pivot hole in the hammer itself.
 
What difference does that make? The rebound spring has nothing to do with the force of the hammer fall.
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But, it DOES directly effect Trigger pull weight. Which is what you provided measurement on. You may be able to increase hammer spring tension (weight) AND LOWER rebound spring weight. Thereby, increasing the energy the hammer strikes with and not increase the trigger pull weight at all.

Gotta balance things...or so Yoda told me:D
 
But, it DOES directly effect Trigger pull weight. Which is what you provided measurement on. You may be able to increase hammer spring tension (weight) AND LOWER rebound spring weight. Thereby, increasing the energy the hammer strikes with and not increase the trigger pull weight at all.
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The rebound spring is already at the lowest offered from the Brownell's series (12 lb.). It is about the lower limit for consistent trigger return.
 
I never cut springs, but take down the OD on them with a belt sander, so they lose some of their tension.
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A belt sander on a spring as small as the cylinder stop spring? I would like to see that.

The rebound slide spring and the cylinder stop spring would not cause the hammer to strike any less harder. That is all in the hammer spring, and what I mentioned above.
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I agree. Both those springs were lightened in the quest for a lower trigger pull weight.
 
I've not measured the differences in the arc of the firing pin to pivot between the different models to know what the exact distances are, but that does come into play. There are changes between the frames in this.
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However, I am under the understanding that K and L frame components are interchangeable. And, the frame size is the same in the instance of my K38 and model 66...both K frames, but the M66's double action is reliable as to firing Federal primers at its 6 lb pull., whereas the K38 is not...even at 8 lbs.
 
But, it DOES directly effect Trigger pull weight. Which is what you provided measurement on. You may be able to increase hammer spring tension (weight) AND LOWER rebound spring weight. Thereby, increasing the energy the hammer strikes with and not increase the trigger pull weight at all.
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My purpose is to lower the double action pull weight to the six pounds or so that I have on the others while having reliable ignition, not just decrease one and lower the other to end up with the same eight pounds.
 
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A couple of good things to look at have been suggested ( and a couple of non sequitur). Thank you for the input.
The things that seem more likely that I have not checked are the suggestion about firing pin protrusion and the rear cylinder gap. I will check these out and report back.
 
I can think of several things that could cause what you are seeing, but let's try just one.

Check to see if the hammer is contacting the rebound slide as it falls. An S&W is set up for a certain minimum trigger pull for reliable ignition. But if the pull is too light, the hammer may fall before the rebound slide is out of the way of the hammer and result in erratic firing. .

Jim
 
A belt sander on a spring as small as the cylinder stop spring? I would like to see that.
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Oh, that is very easy. You place the spring on a small punch/pin, inserted through the center so it can turn, and put them against a belt at a 45 degree angle. It doesn't take long to take down their OD. They spin as they're being ground down, so it is an even reduction all over. It doesn't take long to do this, and you have to watch and not overheat the spring, or take too much off. AGI has a video on this very thing, about S&W tuning.

As small as those springs are, it is easily accomplished.
 
I have discovered that the hammer nose (firing pin), is striking the frame after it enters the hammer slot in the frame. This may be the cause of misfires and the subsequent need for a heavy mainspring tension to achieve reliable ignition.

This circa 1959 K38 does not have a spring loaded hammer nose as do the later models.

And before anyone asks, the hammer nose is installed in the correct orientation (not upside down).

The hammer nose is free to rotate on its rivet.

So, what is the correct "fix" to keep the hammer nose from striking the frame? I have already tried a spring loaded hammer nose and that one struck the frame also, despite the spring tension holding the nose down...I think inertia was overcoming the spring upon hammer release.
 
Is the nose actually supposed to hit the frame? Is it possible that there is a casting/forging flaw in either the frame or the hammer that could be smoothed off?
 
I'd look at your hammer nose protrusion. I'd wager it's lower in the K-38, so it's a little less reliable with a lighter hammer spring.
 
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