So I changed the mainspring on my new SW Model 17


April 11, 2010, 02:30 PM
To the Wolf Reduced Power spring. I went to the range for the first time today and it only ignited the primer probably 50% of the time. Very frustrating to say the least. Now I have to order a stronger spring, take the side plate off again and change the spring. Real PITA.

Just a heads up for people thinking of changing the mainspring.

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April 11, 2010, 03:36 PM
My Model 17, which I received as a gift in June 1992, already had an exceptionally fine action. It's become a wee bit smoother over the years, I think. Hard to discern as it was fine before.
I've never seen the need to swap springs.
However, about a year after I bought it, I noticed it was terribly gunky inside. I removed all the guts (not a thing to do if you're not familiar with the S&W action, but I am) and cleaned and degreased every part and the interior of the frame.
Then I relubed with a high-grade gun oil.
The difference was immediately apparent.
The .22 Rimfire can leave a lot of residue, flecks of lead and lubricant and assorted crud in an action, even those you think are well sealed against such intrusions.
I've done the take-apart cleaning a few times since I've had it, after thousands of rounds. In each instance, the action improved markedly.
But unless you're familiar with the Smith & Wesson action, I'd suggest you have a gunsmith take it apart and give it a good cleaning.
Often, that's all it takes to improve an action -- a detailed cleaning and light oiling.

April 11, 2010, 03:56 PM
This is a brand new model 17. The factory spring was like a wedge of steel, probably 20lbs+ pull.

This one,

Besides that it's a gorgeous gun, I mean really nice.

April 11, 2010, 08:20 PM
I've only purchased two NIB S&Ws, a 686 and a 642. Both came with stiff, gritty DA triggers out of the box. The 642, with a few thousand trigger cycles (dry and live) and an internal clean/relube, had a very noticeable improvement in action quality. Nice and smooth with a clean break. The 686, OTH, is going to need an action job. Though the DA is useable, it leaves a lot to be desired. One of the cruddier pulls of all my revolvers. Stiff, with lots of roughness in the last 1/8" before release.

22 rimfires are particularly sensitive to mainspring tension. My Model 17 (made in '59, bought used in '06) was having a number of light strikes. I figured the mainspring may have had a lot of cycles on it, given it's age, so I replaced the mainspring with an OEM part from Numrich. Now I only experience about 1 light strike per 200 rounds. I can live with that.

You should not dry fire you Model 17, unless you have snap caps or spent cartridge cases. But after pulling the trigger a thousand times or so, you or a gunsmith could clean out the internals and relube. Hopefully, this will take care of the problems you are having with the stiff trigger pull.

April 12, 2010, 06:57 AM
Is your trigger spring tension screw fully in? If it's come loose for some reason there won't be enough tension. But if it is tight you can try adding a hair more tension by putting a thin shim in between the tension screw and the spring. A cut down .22 casing would do as a start and likely that's all you'll need. Cut it down so that it's a short little cup shape that will fit over the end of the tension screw post. If it needs a little more then another common cup shim is a spent primer with the anvil pryed out and the firing pin dimple flattened with a pin punch. The metal of the cup is a hair thicker than the base of a .22 casing.

You can also make your own shims from flat sheet metal such as from food tins or other sources of different thickness sheet metal. The shim for this should be cut in the form of a letter "T". Then bend the base of the T at 90 to sit between the screw end and the spring and then bend the arms of the T around the screw post so it is retained against walking out of place from firing the gun. For this the width of the arms and base of the T should be about 1/8 inch wide. You'd make the T by just cutting the two bottom corners out of a square of metal about 3/8 square.

Also be totally sure that the rounds fit all the way into the chambers. If the chambers get a little dirty from fouling and the rims don't seat fully into the chambers solidly the all important snappiness of the hammer may not set off the primer because of it being cushioned by the round being seated by the first part of the hammer strike. If the rounds fire OK on the second strike after the misfire I'd suspect that this is the case.

Hope you get your 17 working better. I know that I love the one I got recently. In my case I lightened the main spring by just grinding down the stock spring from the flat cross section to one that is shaped like a flat pyramid. I didn't mind doing this since I've got three other stock mainsprings from my other S&W's that were replaced by Wolff kits as backup. Turns out I didn't need any backups though. The 200 to 250 rounds I've shot from my 17 without issue so far tells me I got it right.

April 12, 2010, 07:00 AM
I went through the same thing with a model 66. I had a gunsmith do the work for me. He told me before he started that he is not in favor of changing springs and prefers to just smooth the action. After the third time I took it back we agreed to go back to the stock springs for reliability, I couldn't agree more.

It is now smooth and shoots every time. I will never have springs changed again.

April 12, 2010, 11:03 AM
Thanks BCRider, I'll try that before I switch the spring back.

Jim Watson
April 12, 2010, 11:28 AM
Rimfire requires a harder blow to ignite than centerfire, which calls for a stronger spring. Skeeter Skelton said that was why he preferred a .38 to a .22 for trick shooting.

Your new issue M17 might run on a Wolff standard mainspring.
If it doesn't, the next thing to do is to start recontouring the factory spring (best have a spare.)

April 13, 2010, 07:10 AM
S&W has, in recent years, used both some tapered end strain screws and factory filed/ground screws that, when tightened, intrude into a Wolff spring's hollow back, aka the 'Power Rib'. This lessens the pre-load - and attendant primer hit energy. A replacement screw should bridge the gap, offering more pre-load - and fewer ftf's. I used an Allen headed SS set screw from Home Depot - and some blue Loctite - with my full power Wolff leaf. You turn the screw in until you have the same separation between the leaf and the front of the grip frame. Shoot it - turn it in more, 1/2 turn at a time, until you get no ftf's - then add a quarter turn or so - and a drop of blue Loctite. Don't expect the same low DA pull you can get with a cf S&W - rimfire primers take a harder 'hit' to ignite than do cf primers.

Of course, polishing the innards - and a lighter trigger rebound spring - are required for the best trigger. Don't touch the engagement surfaces - they wear-in in use. Send it back to S&W for the 'best' trigger job.


April 13, 2010, 11:25 AM
I'm with Stainz.
A lighter rebound spring and internal polish does more good for the trigger pull on a Smith and Wesson than that age old quick fix idea of replacing the mainspring.
Polishing the internal surfaces of the rebound and trigger and hammer contact points on the frame do wonders for improving pull weight without sacrificing reliability.

April 13, 2010, 01:28 PM
Excellent info on the power rib issue Stainz. And also some good stuff about the internals.

Part of my treatment on the 17 was to polish the area of the frame where the trigger return block slides. Once into the gun it was obvious that it had not seen a lot of use over the years. The blueing on the cutting took marks was barely touched where the block slides. Also there was a slight burr on one face of the block. A bit of rubbing on my super hard arkansa stone polished the block and a little bit of lapping with some 600 grit polishing compound and a home made lap soon had the block slipping back and forth like a fish on a wet board.

For the trigger return spring I wound my own. Been winding a lot of springs recently thanks to this new gun hobby and a love of tinkering. In the quest for the lightest possible pull I even slightly flattened the angle of the ramps on the trigger return block and the hammer where they engage. This made it easier for the return spring to snap the trigger blocking back into engagement. Mind you I'm on the ragged edge since if the trigger is released super slow it may or may not reset fully. But with any sort of speed to the release it snaps back nicely. But if it acts up in the future I'll need to make and put in a new spring that is just a couple of ounces harder. But hey, the tinkering is half the fun for me.

Here's a pic of the lapping block I made up. I've used it on two of my S&W's so far. The Model 10 that had not been shot much and more recently my 17 which was in the same boat use wise. Looking at the frame you can just see how the crests of the tooling marks were feathered off so that there's a series of nice flats that all line up perfectly for the return block to slide on now. The troughs of the tooling marks between are left both to avoid lapping too deeply as well as surface area breakups to provide places for the gun oil to sit and to break the viscous suction that can result from surfaces that mate a little too well.

Jim K
April 14, 2010, 01:34 PM
I have milled the bottom and left of rebound slides lengthwise down the center, leaving two "rails", resulting in less friction. I found the improvement was so slight as to be not worth the effort (or cost had it been for a customer).


April 14, 2010, 03:19 PM
And I'd expect no big change from doing that either. But leveling and smoothening crests of the tooling marks made the trigger pull very noticably smoother.

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