I recently inherited a Model 66 no dash from My Father. I am not sure where he got it but I do know he did not buy it new. I shot it for the first time this weekend, and before I shot it I noticed the trigger pull was very light. It shot serval cylinders of 357 Magnum without any issues., but it had several light primer strikes and no ignitions with 38 Special ammo. The 357 Magnum was Remington ammunition, you 38 Special was Winchester white box. I have checked the tension screw on the leaf spring and it is adjusted all the way in. I am wondering if the screw has been changed to a shorter one, are filed down to lighten the trigger pull.

Is a longer tension screw available? Do you think this is what I need to do to correct the light primer strikes? Or should I just send it back to Smith & Wesson and let them look at it?

I am very pleased with it overall it shoots very well, very accurate and smooth. Here are a few pics.

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There probably is dried lubricant on the internals which act like varnish. Tear it down as far as possible, clean it with gun scrubber then lubricate it. Youtube is your friend.

I bought a 649 used. It would not reliably fire .38s when used double action. It was full of varnish. Good cleaning and presto, totally reliable.

It never hurts to give a revolver a good cleaning and lube. But I suspect the springs may have been changed. Common thing to do on a handgun used for target shooting. Not so good for a defensive handgun.
One of my 66’s has lite springs. It’s only reliable with my hand loads when I use Federal primers.

Remove the rubber grips so you can make sure the strain screw is tight. The strain screw is located on the front side of the grip frame. It's also a good idea to remove the rubber grips every six or so months, as they will retain moisture, which can lead to rust.

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Always Stay Strong!

I AGREE WITH Seven High. LET'S START WITH A SQUEAKY CLEAN GUN, AND SEE WHERE WE STAND, BEFORE GOING ANY FURTHER.....

A "LUBRIANT" LIKE WD-40 MAY BE THE CULPRIT....

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'Nam 1968-69.DAV,VFW,NRA Inst.

Okay everybody good idea I'll take the side plate off tomorrow and clean it out real good and lube it with some CLP.

Stainless rear sight? I have an early one with that stainless sight. Nothing to add on the light primer strikes but wanted to tell you that’s a nice gun you inherited.

A little trick to try take a spent primer cup ( anvil removed) and place it on top of the strain screw tip and tighten back down. If the misfires go away, you know a longer screw will fix it. I tried this trick many time over the years and often just leave the primer cup in place. A bubba fix perhaps but works

I don't know if you've ever removed the side plate off a S&W revolver but please don't pry it off with a screwdriver. The proper way is to tap the frame with a wood or plastic mallet so that inertia will dislodge the plate. Please use hollow ground proper fitting screwdriver bits to remove the sideplate screws. See YouTube if in doubt. Please disregard my post if you've done this before.

You might consider picking up a set of gunsmith specific screwdrivers. That way you minimize damage to the screw heads.

Ok everyone, I took the sideplate off and cleaned thoroughly, and re-lubed with clp. Still way too light trigger pull. I do not have a trigger pull gauge, but I estimate it is about 2/3 as light as my 640 pro J frame.

I took back to range and still getting several light primer strikes with 38 ammo. Winchester white box and also federal ammo.

Strain screw is adjusted all the way in.

Are longer strain screws available ? Or should it go back to the
Factory ?

I would replace the spring first.
Walt

I WOULD REPLACE YOUR SPRING WITH A NEW FACTORY SPRING......

YOU WILL LOSE THE LIGHT TRIGGER PULL, BUT YOU SHOULD HAVE 100% RELIABLE IGNITION, WITH ANY BRAND OF AMMO........

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'Nam 1968-69.DAV,VFW,NRA Inst.

Having a trigger pull lighter than most J frames is not a good measure. A typical J frame, due to the different internals and the geometry of a smaller frame, will have a trigger pull that is anywhere from not great to "oh my, is this really a Black and Decker staple gun?".

I don't know if the revolver needs to go back to the factory for the exam and work, but I would certainly snoop around for a good gunsmith. If you can't one nearby that you think you can trust, I am confident that member "BMCM" can do what you need, with quality and a fair price. Look for a couple of his strings in the autopistol subforum - he's done some good stuff on 3rd generation pistols. I had him round butt my 4" 66 and I am very happy with the work and the price.

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NHI, 10-8.

It sounds like from what you have said and done so far that the strain screw has probably been shortened. I would order a new spring and screw and be done with it. Fairly cheap parts and a much faster fix than sending it back to the factory.

This sounds like the best solution , I will order them and let everyone know what happens.

Do I need any kind of special tool to change the leaf spring ?

I have a like new Model 25 with this problem. Is there a longer strain screw that can be purchased somewhere? Mine the main spring's shimmed out so far almost interfering with the stocks screw.

If looking for parts google Numrich gun parts. Brownell's also has parts available.

As far as changing the mainspring ( you called it a leaf spring ) ,no special tools. Remove the grips, then remove the strain screw at the front of the grip frame and the spring will have very little tension on it. Then just gently push it sideways out of the slot in the frame. Should come pretty easy.

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1st smiles,lies.Last,gunfire.

You can get a new screw from most Ace Hardware stores. Many of them have a gun screw collection in the little drawer boxes sets. Most of them are long, but have correct threads and a variety of heads. Uses calipers and a grinder/file to adjust length. Slightly round the tip portion after grinding.

I have a lot of taps. With small screws I usually tap a hole in piece of brass and use it to hold the screw while working on it.

I never had that problem with the used Smith Revolvers I picked up. THEN, I picked up a 2" 10-5, RB. Had the light strikes. Changed the strain screw, and problem solved. (it had been shortened) Bought a K, 10-6, PPC, that was the same way. New screw, problem solved. Bubba knows how to shorten strain screws. Bob

Why order parts that you are not sure you need?

Shortening the strain screw is the most common thing done to lighten trigger pull.

Measure yours, post the results here so it can be compared, and then you will either know that is the part that needs to be replaced or eliminate it as the culprit.

It's not just Bubba who shortens strain screws. In his Youtube video on installing spring kits Jerry Miculek tells the proper way to shorten the strain screw. Skip to 4:30 for that part.

I just bought the super duper 58 pc +/- Brownell set, and I could not take a side plate off an old model 12. Bought the GRACE HG7, 7 driver pistolsmith set for like 32.00. Go that way first. I got mine from Optics planet. save yourself 90.00

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Pete
I ain't no fortunate son

BTW, lots of old timers used to shim the strain screw with a thick piece of leather.

It smooths the action a little and in your case might give enough extra oomph to fix your problem.

One other thing that you might try is to put on a set of wood grips. Some brands of rubber grips put pressure on the mainspring when installed, which causes erratic firing.

The strain screw in my M-66, with the stainless steel sights, is 0.475" from the base of the head to the tip of the screw. The tip should be evenly rounded with no machine or file marks. If yours is shorter than this, replace the screw. If the screw is ok, replace the mainspring with a standard weight spring. If this doesn't fix your problem, let us know & we can explore less likely issues that may be causing misfires.

I have used a leather pad between the mainspring and the frame on a Colt single action revolver. This was done to lessen the strength of the spring.

The spent primer cup on the end of the strain screw, mentioned above, lengthens the screw to increase the hammer fall.

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John 3:16
WAR EAGLE!