If you’re going to smooth a revolver’s internal surfaces and then use strain screw length to set a particular double action pull, does the main spring type (factory, Wolff type 1, or type 2) really matter?

Does the geometry (curved vs. straight) of a main spring have any significant effect on double action pull? For example, is a curved reduced power spring with a longer screw the same as a flatter factory spring with a shortened screw, if both are set to say 9lbs? Or is a wolf type 1 spring better because of the power rib, than a factory spring, if both are set at 9lbs?

All that is normally required to an older Smith (sorry, not familiar with any modern MIM guns) is to completely disassemble, clean, de-burr - only the minimum required, replace Rebound Spring with a 13 pound Wolff spring, slightly shorten Factory Strain Screw to lighten the Factory Main Spring, properly lubricate and reassemble. NEVER NEVER stone or alter Trigger/Hammer engagement surfaces as that is the fastest and surest way to ruin a Revolver. Never leave a full length Strain Screw loose. Assuming there are no manufacturing abnormalities that should do it. Shoot the heck out of it and you will have a smooth revolver action.

Exactly how much is required to shorten the Strain Screw varies slightly from gun to gun depending on that particular Main Spring. It's something you just have to develop a feel for. Buy a few extra so if you shorten one too much you have others as a back up. I have never found it necessary to replace the Factory Main Spring and in fact dislike many of the after-market ones - I don't care for their hollow twangy sound either. Slightly shortening the Strain Screw has always worked for me - make sure it is tight!

Use a good lubricating oil sparingly and do not flood the gun with oil or it will be dripping out for weeks to come. Dry firing with snap-caps or empties will also greatly speed up the smoothing process.

Absolutely, yes. When I put the ribbed spring in a competition revolver, I use a grade 8, 8-32 screw and grind it to the length I want, which is usually longer than the stock strain screw for the stock spring. You can shorten the stock strain screw somewhat with the stock spring, but overdoing it causes geometry problems.
Having suffered through metallurgy class, I don't completely trust any spring that has been re-bent after being tempered. The bent point becomes hardened and more brittle, and you can't really tell how much.

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Science plus Art

The Wolff springs (both the type 1 & 2) have the rib indentation running down the length of the spring, and in the round butt grip frames, it will need a longer strain screw, otherwise you will be prone to light primer strikes. which is exactly what happened on my 625-8 JM.

A few weeks later while I was still mulling over what to do next on the 625, I bought a 986 Pro Series, which is an L-frame 9mm revolver, that S&W advertising boasts about it sporting a Performance Center mainspring for a lighter and consistient DA pull.

I was curious what a Performance Center mainspring looked like, so I opened 'er up... Well I'm here to tell you that it looks exactly like a Wolff type2 (reduced power) spring... hmmm, what are the odds that it isn't one?

And I also discovered that the strain looked different and familiar, the factory used the longer style strain screw for a square butt frame gun to compensate for the rib recess in the spring.

So I ordered one of those longer strain screws. When it arrived I measured its length against the one in the 986 and they were identical.

I popped that puppy into the 625-8 and problem solved.

As a measure of insurance against hard primers, I also installed an APEX XL firing pin kit, which has a longer travel and a reduced spring.

I took the 625 out to the range, I fired CCI and Winchester "White box" ammo, both known to be prone to FTF's with lightened main spring setups. No problem except for a couple of the Winchester rounds, which I attribute to the reputation of "white box" ammo, since many people have experienced FTF issues with it in out of the box stock guns.

Your question about the main strings with the different curve, my understanding is that is more so for a consistent feel (no spring stacking towards the end of the DA pull) than contributing to lightness. Jerry Miculek mentions that in his "Trigger Job" DVD regarding his BANG spring kit.

Everything Chief38 has said is spot on.

And with the frame mounted firing pin guns, just like on a S&W semi-auto pistol, the firing pin spring is balanced with the power of the hammer mainspring. When you go lighter on the mainspring, you need match the firing pin spring to it or you'll be fighting with misfires.

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Conrad
SWCA #1830 SWHF #222

Yes. Whatever combination you use, it is a dance of thousandths between the trigger pull weight you're aiming for, too much, too little, and misfires.

Go slow, and test your loads at length if you're going to trust your life to the revolver in question...

Something to keep in mind is that a lot of what you read on the Net is Rumors endlessly repeated. For example the CCI Standard primers are NOT nearly as "hard" as the net would lead you to believe. In fact I've found the are about equal to Federal primers for sensitivity. For Standard primers the brand I've found to be harder to ignite are those used in Remington UMC ammunition.

Note, the CCI Magnum primers are a different story. Because they are distinctly "harder" than either the Standard CCI, Federal, or even Remington. If you want a good test to insure reliable ignition either reload with CCI Magnum primers or look for some Blazer 357 Magnum ammunition.

Tomcatt51 also points to the basic Physics involved in Primer Ignition. That is that this is a process of Kinetic Energy Transfer and if you remember your Classic Physics Kinetic Energy is equal to 1/2 Mass times the Square of the Velocity. So, the weight of the hammer installed in your revolver can be a critical factor in how light you can "tune" your trigger. Tip here is to avoid the Target Hammer and instead look for that old narrow 0.265 inch wide Service Hammer. BTW, at times I've considered having a Titanium Hammer made up just to see how light the action in a modern S&W could be tuned.

Then there is the matter of the firing pin projection through the recoil shield. One distinct positive for the newer firing pin in frame design is that it does permit one to easily change the length of the firing pin. However, one has to be careful with this approach because a firing pin that is too "long" for a heavy hammer strike can result in a pierced primer and a firing pin stuck in that primer. BTW, if this does happen the correct way to get it free is to GENTLY rock the cylinder side to side until the firing pin pops free.

What all this means is that properly tuning the S&W medium and large frame lockwork requires a Balanced approached. Because if you want to tune a 357 Magnum you may need to use a different approach than what you would for a 38 special. In addition because the hammers for the N and X frames are a bit larger than those for the K and L frames you may need to put a bit more power into the mainspring to get those heavier hammers moving fast enough. Finally, it's been my experience that the new MIM lockworks are actually easier to tune than the older models becaust the parts are just so darned consistent for size and contour that you almost never have to do an "fitting".

PS; currently I'm working at getting reliable ignition with Magnums in a recently acquired 19-3. Problem is that the Hammer Nose is about 0.015 inch short by the "dime test" and if tuning the trigger to 9 lbs. 8 ounces doesn't resolve the misfires I'll have to order up a Powers Custom extended Hammer nose and hope the post 1988 spring style nose will work in my 1971 vintage model 19.

The '71 hammer's rivet throughway is higher than the post '88 hammer's, where the throughway is drilled lower to accommodate the spring. The new firing pin might not align properly with the firing pin hole. Keep us posted.

Thanks for the input everyone, I think I’ll go with the reduced power spring and longer screws (have some coming from ebay), and then adjust length for around 9 lbs.

My first attempt at a trigger job using the Miculek DVD was a 66-3 RB. Internal smoothing took the DA trigger pull down to about 10lbs 5oz with factory springs. Changing the springs to a reduced power and 14oz rebound brought it down to 8lbs 9oz, but with about a 30% misfire rate using my CCI primed reloads.

The strain screw should never be modified . . .

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Wisdom comes thru fear . . .

For a designated target gun I see no reason at all the Strain Screw can not and should not be modified. There are many many in the target shooting community that do this with great success and with no risk at all to the gun. Strain Screws are readily available, cheap, and can be ground to the perfect size for ones specific needs and purposes. A Revolver can always be fully restored in a few seconds by re-installing the original and all is back to Factory spec's.

Factory length Strain Screws are made to that size strictly for reliability - NOT a light trigger pull. I have many Range ONLY guns that I have done so with and it vastly improves both SA & DA trigger pulls without a single misfire! Yea, in the beginning I might have gone too far when cutting one, so I throw it away and start fresh. Now I go by "feel" and can usually dial in a Smith within minutes and can't remember the last time I went too far, but again they are cheap enough..... One can purchase a dozen to keep on hand without breaking the bank, and KEEP THE ORIGINAL available if and when the gun is either sold, traded, or used for self defense purposes.

Why? Do you think there's a curse that befalls all who would dare defile such a sacred relic?

Even for "Duty" guns S&W had a procedure for armorers of clipping the rebound spring (or using the blue spring from the SAO 14) and shortening the strain screw for a lighter DA pull.

'Well you guys got some different ideas for some pretty standard jobs. Let's see. Why not weigh your hcammers like gunsmiths do using a standard trigger pull gauge

Factory:
357 mag: 56 oz
38 sp : 52 oz

Custom Shop:
357mag: 42 oz
38 sp: 38-40 oz
Target hammer: 44 oz with stainless spring
Old style target hammer w/ blue spring 52-54 oz
K frame rimfire: 40-42 oz.

Older hammer noses must have good springs
Moon clips too much variables fire testing required
Stainless springs are a bit stiffer
These settings are never full proof but close.

Of course I built comp guns for plates and pins or Bullseye so unlike many owners who shoot a range of bullets and loadings we dial in the mainspring for a load. Competition loading is very specific since any variable is unwanted. One of these variable is primers. Despite what some here might think everybody I knew including Ron Power, Clark etc wants to know if you're shooting CCI primers or Feds. At gunsmith school you were instructed to add a couple oz for CCI primers. Maybe it's BS but it's factored into the equation. Once established the gun is tweaked for reliable performance with the comp load.

And yes the main spring screw is filed to length for the load and spring. Once the spring weight is established the screw is trimmed then screwed all the way home, tested with live ammo in rapid DA and if correct removed, a drop of blue Loctite on threads and screwed all the way home to remain. Different screw length for different loadings and mainsprings. These screws go in the gun's swap parts box and are color coded to match springs. Main springs from the factory are worthless for building a good smooth DA comp gun. There are many variables from length, width and thicknesses which means batches and the question are they out-sourced ? Almost all, though some are much much worse, have numerous stress raisers all of which concentrate or interrupt uniform loading and strain along the spring.

Wolff springs are an improvement but still create a wavy pull-thru in DA. I mean an experienced shooter will feel the uneven pull force on the second half of the trigger pull. It may not be a lot or even discerned by a new shooter but it's enough to affect the front sight in match shooting and something a competitor has to allow for. I personally can't understand the dynamics and load dispersion of the Wolf main springs and the humped centerline rib. I recall asking once years ago at a Shot-Show and was told its proprietary. Okay but how does it work ? I quit using them once Ron Power showed me how to grind, polish and reshape springs. It takes some practice, some good wood shaping blocks and hammers but the results when done right are worth it. This type of spring is the primary reason Colt mechanics are so rare. Flat springs are an art of their own and without them Colts don't work. The S&W mainspring is no comparison. A reshaped or mainspring when done right loads up pretty much evenly through the whole double action pull.

I pulled out some done springs and others. The two left and are custom for a 686 plate/pin gun and a 625 Pin gun, third is a Wolf and finally a factory L.

Attachment 213557

Regards

Guess that chapter got skipped when I was last in Springfield . . .

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Wisdom comes thru fear . . .

Things change. Some things that were recommended aren't anymore due to liability fears and being PC.

I just now discovered that my uploaded image of the springs disappeared why I don't know ?

Here it is again
Two custom reshaped polished springs on left
Standard Wolf
Factory stock spring on right

image.jpg

Would you be willing to post or point the way to a tutorial?

Just a followup. Installed that Power Custom hammer nose kit in my 19-3 and the only fitting required was to reduce the length of the firing pin by about 0.015 inch. I'll also note that the instructions for fitting this hammer nose were superb. They provided clear illustrations and instructions for the fitting points designed into the new hammer nose so that the striking position for the hammer nose on the firing pin bushing.

Note, my model 19-3 now works perfectly with CCI 550 Magnum primers with the Strain Screw restored to it's original length and a DA trigger pull of 8 lbs. 9 ounces. I also have a "light" Magnum worked up for this snubby that is both a pleasure to shoot and won't do any damage to the forcing cone.

garbler, if you are willing to share some of your tuning info, especially about springs, you have a captive audience.