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I'm guessing those of us in never never land have lighter actions than scooter123. Don't know for sure though.
Best way to raise mainspring tension?
- Thread starter matteekay
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scattershot
Member
New strain screw. If you can't get one before your match, use a leather pad between the screw and the spring.
I am completely baffled by your results of an insignificant change in trigger weight.
I have been tuning mine and family and friends S&W revolvers for about 30 years now.
My method is always to take off the side plate and stone any rough metal to metal friction points smooth.
The result of the stoning is very smooth action, butter smooth, no gritty feel. The difference in trigger pull weight is negligible over a 10 pull average.
If I or they want lower trigger pull weight, I replace rebound springs until I cannot get further reduction and I still have reliable function or until I or they are satisfied.
At every step I use my digital lyman trigger pull gauge to keep track of changes.
The drop of double action trigger pull weight reduction is very significant.
My 27-2 went from 12 pounds to 8... My 29-2 went from 13 to 7.
These were probably the 2 largest differences between before and after rebound spring change.
But, with the other approximately 25 or so S&W revolvers I have worked on, there was always appreciable trigger pull weight reduction.
That is why I am so baffled by your result.
Doc
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bountyhunter
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The mainspring and RB spring should be tuned as a set: when you get the mainspring where you want it, install the lighter RB spring (or clip it) until you have just enough spring force for good trigger return. DA Triggers of 5 - 5.5# are attainable with soft primer ammo, DA pull more like 6.5 - 7# if you you want "headroom" for popping reluctant primers. And yes, the RB spring affects both DA and SA pull.
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scooter123
Member
Doc, I expect that you are reporting the result of a complete tuning, IE mainspring being replaced/re-tensioned AND Rebound Spring being replaced at the same time. Don't blame you a bit for that because it is the most efficient approach to tuning a S&W revolver.
I am a Mechanical Engineer by training and temperment, so at times I'll take an approach that some regard as a complete waste of time. However by nature I like to "figure out" how things work and rather enjoyed the Design of Experiments classwork in college. So when I first started tuning my model 620, the very first revolver I tuned I started out by replacing the Rebound Spring and doing nothing else. What I found was that changing the Rebound Spring had very little effect on the DA trigger pull at break but did have a noticeable effect on the SA trigger break. Now I'll admit that I didn't keep my notes and should have, but my memory is that going from the factory Rebound Spring to a Wolff 14 lbs. Rebound Spring only reduced the DA trigger pull by 4-6 ounces. Further testing revealed that by shimming the strain screw I could see a distinct and noticeable change in the DA trigger pull with almost no change at all in the SA trigger weight. Final results were that I determined that most of my revolvers could be tuned to an 8 lbs. DA trigger with a 3 lbs SA trigger by shimming the strain screw by 0.03 inch and installing a 14 lbs. Rebound Spring. I also discovered that such a shotgun approach won't work with every revolver but it will get you close.
Note, I have made up shims for the Strain Screws on my revolvers because as an Engineer I like things to have some adjustment and doing so allowed me to re-adjust all of my revolvers when I determined that Remington primers have become a bit "harder" in the past couple of years.
Now, I know some won't believe what I'm saying. To those doubters I would suggest you take one of youre Tuned revolvers and do just one thing. That is replace the Rebound Spring and leave every other item unchanged. Then measure the trigger pull. Do that and you will find that I am actually correct. The rebound spring has very little effect on the DA trigger weight but does have a noticeable effect on the SA trigger weight.
I am a Mechanical Engineer by training and temperment, so at times I'll take an approach that some regard as a complete waste of time. However by nature I like to "figure out" how things work and rather enjoyed the Design of Experiments classwork in college. So when I first started tuning my model 620, the very first revolver I tuned I started out by replacing the Rebound Spring and doing nothing else. What I found was that changing the Rebound Spring had very little effect on the DA trigger pull at break but did have a noticeable effect on the SA trigger break. Now I'll admit that I didn't keep my notes and should have, but my memory is that going from the factory Rebound Spring to a Wolff 14 lbs. Rebound Spring only reduced the DA trigger pull by 4-6 ounces. Further testing revealed that by shimming the strain screw I could see a distinct and noticeable change in the DA trigger pull with almost no change at all in the SA trigger weight. Final results were that I determined that most of my revolvers could be tuned to an 8 lbs. DA trigger with a 3 lbs SA trigger by shimming the strain screw by 0.03 inch and installing a 14 lbs. Rebound Spring. I also discovered that such a shotgun approach won't work with every revolver but it will get you close.
Note, I have made up shims for the Strain Screws on my revolvers because as an Engineer I like things to have some adjustment and doing so allowed me to re-adjust all of my revolvers when I determined that Remington primers have become a bit "harder" in the past couple of years.
Now, I know some won't believe what I'm saying. To those doubters I would suggest you take one of youre Tuned revolvers and do just one thing. That is replace the Rebound Spring and leave every other item unchanged. Then measure the trigger pull. Do that and you will find that I am actually correct. The rebound spring has very little effect on the DA trigger weight but does have a noticeable effect on the SA trigger weight.
tomcatt51
Member
I have a 686-5 set up for silhouettes, IHMSA FPAS. The rules are pretty resrictive as to what can be modded.
It has a stock mainspring, the original strain screw fully tightened and an 11 lb rebound spring.
I use a Lyman digital gauge. I measure with the gauge held so the rod to the trigger runs parallel to the barrel bore and the roller sits on the trigger where it wants to.
The trigger pull originally maxed out my Lyman digital gauge. 12+ lbs. The stock mainspring / strain screw, 11 lb rebound spring combo gives an 8 lb 1 oz DA pull and a 2 lb 6 oz SA trigger pull. It takes a 7lb 10 oz pull to get the trigger to start moving DA (the "initiating force"?). The trigger returns consistently but this is not a combination that can be shot fast DA. The trigger simply doesn't return fast enough but the gun was set up (within "production" type rules) for shooting silhouettes SA.
I checked one of my 627s. Wolff reduced power mainspring, socket set screw as a strain screw, 11 lb rebound spring with ~3 coils clipped. 5 lb 4 oz DA pull (it's DA only) and it takes 5 lb 2 oz to start the trigger moving. This gun runs just fine shot fast DA action. I've also run it in the low 4 lb range with a little more tweaking. I stopped there and went back to low 5's.
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Doubling back to the original problem child...
I put a new strain screw in last night and the pull only went up about 3 ounces - I guess the one that was in there wasn't filed as much as I thought. So, I added the Wolff Power Rib Type 2 mainspring and that added about a pound (as expected). In double action, I went from 7lb 14oz to 9lb 3oz on average. The pull isn't too much worse and it should ensure I get ignition until I can start loading my own ammo. I'm also ordering the Power Customs extended hammer nose for a little extra insurance.
I put a new strain screw in last night and the pull only went up about 3 ounces - I guess the one that was in there wasn't filed as much as I thought. So, I added the Wolff Power Rib Type 2 mainspring and that added about a pound (as expected). In double action, I went from 7lb 14oz to 9lb 3oz on average. The pull isn't too much worse and it should ensure I get ignition until I can start loading my own ammo. I'm also ordering the Power Customs extended hammer nose for a little extra insurance.
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tomcatt51
Member
Looking at those numbers it sounds like you have a pretty heavy rebound spring. Seems there is a reduction to be gained by going lighter but how light will be dependent on how much internal work has been done and the need to keep a balance with mainspring tension.
I use Wolff Reduced Power Mainsprings in my 7 1/2 lb full hammered "fires everything" guns with an 8-32 socket set screw for a strain screw and a 12 lb rebound spring.
People frequently have issues with the Wolff reduced Power mainsprings. The stock strain screw is often just too short to work with that spring. Easy to fix with a socket set screw and you get a better result, unless you're an engineer I guess....
So even with the pull I currently have, you think there may be ignition issues?
Couple of thoughts about the light hammer strikes......
I didn't see in the previous posts where you mention if these light strikes are during SA or DA. I notice you have a trigger stop installed. Is it possible that the rebound seat on the hammer is hitting the hammer seat on the rebound during firing? Proper clearance between these two seats is necessary for the hammer to come fully forward when the trigger is pulled fully to the rear.
If the trigger stop is adjusted too far back, the trigger may be getting back far enough for it to cam off in DA and work in SA, but not far enough for the hammer seat on the rebound slide to be back and completely out of the way. You might double check to see that there is some gauge between the hammer seat and rebound seat when the trigger is pulled fully back, and the hammer is fully forward. Even slight contact here can impede the hammer enough to cause a light strike. It would be more of a problem during DA firing, as the trigger is not required to come back as far for the hammer to cam off, and move forward. (fire)
Also, I didn't read anywhere that you had checked the rear gauge (headspace) on the cylinder to confirm that it is within spec at .060"-.068". (closer is better, especially when fitting a gun you are using for target)
I didn't see in the previous posts where you mention if these light strikes are during SA or DA. I notice you have a trigger stop installed. Is it possible that the rebound seat on the hammer is hitting the hammer seat on the rebound during firing? Proper clearance between these two seats is necessary for the hammer to come fully forward when the trigger is pulled fully to the rear.
If the trigger stop is adjusted too far back, the trigger may be getting back far enough for it to cam off in DA and work in SA, but not far enough for the hammer seat on the rebound slide to be back and completely out of the way. You might double check to see that there is some gauge between the hammer seat and rebound seat when the trigger is pulled fully back, and the hammer is fully forward. Even slight contact here can impede the hammer enough to cause a light strike. It would be more of a problem during DA firing, as the trigger is not required to come back as far for the hammer to cam off, and move forward. (fire)
Also, I didn't read anywhere that you had checked the rear gauge (headspace) on the cylinder to confirm that it is within spec at .060"-.068". (closer is better, especially when fitting a gun you are using for target)
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These are all double action. I believe the clearance is good on the stop as I fired 100+ other rounds DA during the same match without issue (to say nothing of the hundreds I've fired before that) but I'll definitely check. The most interesting thing to me is that they all came out of the same box of American Eagle, and cartridges from every other box have lit off without issue.
I didn't even know about checking headspace - I'll have to look into that. The one thing I've noticed on this particular gun is that the ejector is fitted with an Aristocrat extractor rod collar and it seems to give the cylinder a tiny amount of front-to-back play. Not actually sure if that's the cause but I can wiggle the cylinder a tiny bit forward and back in when in lockup.
tomcatt51
Member
Wolff Type II, reduced power, with a stock strain screw and Federal primers you're probably ok but this isn't engraved in stone. Bear in mind the length of "stock" strain screws seems to (randomly) vary somewhat. If you want to be sure use an 8-32 socket set screw instead of the (junk) stock strain screw. You'll have the ability to adjust plus the tip won't deform like the stock stainless strain screws do. Run the set screw in 'til you get the same gauge reading you had and then you can adjust (easily) as / if required. I file a small notch in the socket end so I have a reference for re-installing / adjusting.
IF you feel you must use a S&W strain screw the carbon steel (blued) ones are much better. Part of the "problem" with the Wolff mainspring is that the tip of the strain screw sits IN the springs' rib so the screw is effectively shorter. That along with the stock stainless strain screws' tips deforming as they're made from a poorly chosen material / heat treat combination.
Nice looking gun.
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tomcatt51
Member
Since you're using the ribbed Wolff spring DON'T file it flat, the angled tip will sit in the rib nicely.
Headspace is around .064". If I use washers to correct the excessive end shake, won't that increase the headspace? Should I just try to split the difference?
The cylinder should not "touch the forcing cone when closed". It should be at least .004"-.006" on a PPC style revolver firing lead bullets/wadcutters. This will help prevent the inevitable build up of shooting debris on the cylinder face from causing binding and rotation issues.
Adding shims to the yoke (or stretching) will move the cylinder back, closing the gauge in the rear (headsp) and opening the B/C gap. Keep in mind, some "end shake" (.001"-.002") is necessary to accomodate lubricants, and for the cylinder assembly to rotate and interface properly.
Adding shims to the yoke (or stretching) will move the cylinder back, closing the gauge in the rear (headsp) and opening the B/C gap. Keep in mind, some "end shake" (.001"-.002") is necessary to accomodate lubricants, and for the cylinder assembly to rotate and interface properly.
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Got it. Well, that sounds like a clear path, then!
I'm wondering if this all started when I had the cylinder cut for moons. I don't remember this much end shake play before that. Could just be my imagination, though.
I'm wondering if this all started when I had the cylinder cut for moons. I don't remember this much end shake play before that. Could just be my imagination, though.
If you need shims, this is a good place to get them. Free shipping.
TriggerShims Brand Shim Kits
The moon clip cut may change your ideal, or proper "in spec" headspace. I would contact whoever did the work for an opinion, or if you have further questions.
TriggerShims Brand Shim Kits
The moon clip cut may change your ideal, or proper "in spec" headspace. I would contact whoever did the work for an opinion, or if you have further questions.
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