Tips on grinding down a S&W leaf mainspring?

[DHart]

I've read that using a bench grinder is a good way to lighten the leaf mainspring on a S&W K/L frame gun... trimming the edges, not the flat part.

Are there any more detailed tricks/tips I should know before I lay my leaf spring up against the grinder?

 

[dfariswheel]

Best advice......DON'T.

Mainsprings that have been ground have a bad habit of breaking later due to internal stresses caused by the grinding.

I'd advise just buying a new, lighter spring from Brownell's.
http://www.brownells.com

New light weight springs are available from a number of makers from Brownell's, and prices run around $17.00.
Another plus, there's no risk of grinding too much and ruining the spring.

 

[Standing Wolf]

I'll second that and add that I've had excellent success with Wolff springs: http://www.gunsprings.com

 

[DHart]

Sounds like good advice. Thanks...

 

[mete]

First , contrary to some the main spring screw is not an adjustment screw for trigger pull. It should always be tight. IF you want to reduce pull then trim down the sides of the spring. Don't use a grinder, a file will do. Remember that smooth is more important that light .There has to be a balance between the mainspring and trigger return spring. Trimming the mainspring should be the very last thing you do in a trigger job.Smoothing every part is important and smoothing the sear and sear notch in the hammer are not for amateurs ! My M29 has a 2 1/2 lb single and 9 lb double action pull. It is VERY smooth and totally reliable.

 

[DHart]

I bought my 2 1/2" model 66 in the mid eighties. It's not been fired much in all these years. THe action is smooth as butter and very light. I recently bought a used model 65-5 which had a considerably heavier action, but still pretty smooth. Just for fun I decided to swap parts between the guns to see if I could make the 65 as light and buttery as the 66. Turns out the only part I have to swap to achieve this is the mainspring. As soon as I put the mainspring from my 66 into my 65, the 65 felt like an entirely different gun. Both mainsprings are stockers and at casual observation appear identical. But on close observation and measurement, the spring from the 66 is a tad bit thinner... making for the difference in trigger pull. It appears as though S&W used a slightly lighter weight mainspring back the the mid eighties than they used when the built my 65-5 some years later (any idea when the 65-5 was built?).

So I know now that I can make this 65 feel just as nice as my 66 does by simply installing a slightly lighter mainspring. I will order one from Wolff, but just for fun, perhaps I'll slim the stock spring down just a tad to see what happens. These smiths are sure wonderful revolvers! I especially love this 3" 65... what a perfect defensive .357 this model makes!

 

[jed]

SW mainsprings

I ordered the mainspring with lower power from Wolff and also got the trigger return springs in various weights.

I replaced only the mainspring and was partially satisfied.

I then opened the side plate and discovered that changing out that spring would not be worthwhile and thus decided to leave well enough alone.

The lighter mainspring still gives reliable ignition after about 500 rounds of testing. However, I don't want to mess with trigger return springs.

 

[870]

As far as changing the rebound spring, do it, but use a 14# one.

That's the one I use, but i have stopped installing the lighter mainspring when I had some missfires with Federal primers and ammo.

870

 

[Dave Sample]

I have adjusted trigger pulls on S&W's for years with the "Strain Screw" just like it says in the S&W shop manual. It works just fine for me. I prefer to go through the gun and do all the things you have to do to make a nice Model 66 wonderful, but I have only done a hundred or so. I did all the State Trooper "66's that worked out of Trinidad Colorado years ago and they didn't have any complaints. I ended up with two of them when they changed to another model for $100.00 apiece. I love all the experts we have on the forums. They seem to know much more than those of us who are in the business of working on various kinds of pistols. I like the 14LB spring in the rebound slide, too. But what do I know? Tuning a Model 66 used to be about three hours for me. Milt Morrison can do one in 30 minutes. Old and slow me.

 

[DHart]

Dave... for a quick and easy effect I'll try backing out the strain screw a little. Yes, some have said that's not supposed to be done, but if it works well and is that easy with no ill effect, it sounds like something to try until I can get a proper action job done. I do have the Wolff reduced mainspring and rebound springs kit on the way... will give that a try also... of course with lots of function testing thrown in for good measure!