I picked up a 29-2 in decent shape awhile back, and noticed that its mainspring is different from my later 629 and other n-frames in that it is much narrower for its full length. The sides of the spring are bare steel, not black like the rest of the spring, almost like they were ground down. I've got several new oem S&W mainsprings that are much wider. I put one in the 29-2 and the trigger pull became extremely (horrendously) heavy and no longer smooth, and felt like there was something wrong with the gun. Are all model 29 oem mainsprings identical? Has someone monkeyed with the mainspring? Thanks.

Your spring is almost certainly ground down from a stock spring, based on your description. If the gun fires reliably with the modified spring in place I'd leave it in and enjoy the benefits of a lighter, smoother action.

Before lower power aftermarket springs were available, people did narrow the spring to lighten trigger pull.

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A standard mainspring that hasn’t been ground down as I described above puts the double action pull at over 15 pounds (closer to 17.5). I tested the mainspring weight as described in Kuhnhausen’s manual, and it is around 7 lbs, twice the 3.5lbs that the manual recommends for a 357. If I understand everything I’ve read about the strain screw and the mainspring, the strain screw often must be fitted to the revolver, and every gun is different. I experimented with turning the screw out and tested the mainspring weight and found that 3/4 of a turn out gives me a DA pull of around 11.5lbs and a mainspring weight right at 4lbs. I’ve ordered several new strain screws and plan to shorten the screw to yield proper pull and mainspring weight when fully tightened. The manual says nothing about the mainspring weight for a 44 Mag, but I am assuming it will be similar to that for a 357. With the screw backed out just 3/4 turn, the DA feels smooth and similar to my other, unmodified S&W revolvers. I’ll test fire and confirm proper function. Does this seem like the correct way to remedy the problem, since I’m definitely going to use a full power mainspring?

Picking a nit perhaps, but can we refer to a stock mainspring coupled with a shortened strain screw as a "full power mainspring"? I think not.

As an aside, I installed a Miculek Spring kit (with anything but a "full power" mainspring), and then shortened the strain screw .090" for a double action pull of 7 lbs. (the minimum recommended---and then only with Federal ammo/primers). It eats anything so far---perhaps suggesting I'm in need of a new trigger pull gauge.

Ralph Tremaine

My way of doing it goes like this. Replace the strain screw with a #8 - 32 x 1/2" long set screw (headless). Start out too light on the mainspring tension.

1. Go to the range and shoot your ammo (the primers you will be using), and dial the tension up in 1/8 turn increments until there are no more light strikes. Then add another 1/8 turn for insurance against that 1 in 100. If you are shooting later and have a misfire, turn it up another 1/8 turn. Measure the hammer pull (not trigger pull, just the hammer) just where the hook comes off the frame with your trigger pull gage and record the number of ounces. Save this number and the gun it relates to for future reference. The brand of primers you're using will determine how light or heavy this number is.

2. Take out the set screw and put blue Loctite on it and put it back in, duplicating the previous hammer pull weight. OR file a stock strain screw to duplicate the hammer weight with the head tightened firmly.

3. Then try different rebound springs to find the one that returns the trigger the way you want it. Some people will want the lightest possible, some will want the hardest return, some will want something in between.

By tuning this way, you will get the lightest action that works how you want it, not just what someone else gives you. You are in control of the process, and it only costs a few bucks for a setscrew and allen wrench and a rebound spring assortment.

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protocalldesign.com

If there are grind marks on the side of your mainspring that are perpendicular to the spring, those grind lines set up fracture zones and the spring will eventually and prematurely break. They should be polished out completely.

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Jim
S&WCA #819

I have heard that. I am trashing the modified spring and putting a new one in with a properly fitted strain screw.

You should carefully evaluate the trigger with the ground spring vs the new spring, both at the level you are just happy with the primer strike. A skillfully-ground factory spring alters how the spring stacks, potentially resulting in a nicer feeling DA.

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Mark

If you don't want it, mail it to me. I have a M27, converted to .44 Special, that has a mainspring in it that I ground years ago and it is still running fine.

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John 3:16
WAR EAGLE!

It turns out there was no need to do any fitting of the strain screw. As you recall, I installed a new OEM mainspring and, with the full length strain screw fully tightened, the DA trigger pull measured nearly 17 pounds. This was immediately after installing the mainspring. After letting the gun sit for a couple of days with the new spring installed, and dry firing it some, the DA trigger pull is now right at 12 pounds and smooth. Odd, but I’ll take it.

Springs, once tensioned, will take an initial set. 12 pounds DA is spot-on for a S&W revolver.

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VCDL, GOA, NRA