Best way to raise mainspring tension?

matteekay · Aug 17, 2016

Hey all,

I used my tuned/PPC model 10 (7.9ish pound pull) at a USPSA match tonight and suddenly started having lots of ignition failures with factory Federal ammo. I have an ICORE match this weekend so I want to ensure everything goes boom for that; I figure the best way is to raise the mainspring tension a bit.

I have two options available: swap the spring in there out for a Wolffe (raises the pull by about a pound) or I can pull out the filed down strain screw and replace it with a new, full length one that I can then file a bit. I have the parts for either.

Would one way be preferable over the other? Ultimately I'll be reloading and this shouldn't matter but for now I need something that works.

Dr Denby · Aug 18, 2016

Hey, Matteekay

I would first put in the strain screw. S&W has that spring/screw relationship down to a science.

It will definitely give you the reliability you are looking for.

Just out of curiosity, have you tried different rebound spring weights?

That is what I would do for trigger pull adjustment. Not fool around with the mainspring and screw when reliability is a key factor such as for competition.

That and taking off the side plate and checking for friction point rubbing. Look for marks in the plate and frame where metal is rubbing metal and take a fine stone to the rough spots/burrs.

Doc

scooter123 · Aug 18, 2016

Doc, changing the REbound Spring has almost no effect on the weight of the Double Action trigger pull, that is set by the mainspring tension. As for adjusting the Strain Screw, that is something that has been used to "tune" the DA trigger weight since the first Hand Ejector was introduced. It's even done by the S&W factory, so it is a "factory" procedure.

BTW, I have a 1972 vintage 19-3 that was originally built with a "short" hammer nose and I suspect misfire problems are why it was nearly unfired when I purchased it. As for why I came to that conclusion about how much use it has seen, it's because the recoil shield was completely unmarked except for a light drag mark showing the cylinder had been opened. Good news is the installation of a Power Custom hammer nose completely solved the misfire problem and the original factory DA trigger pull weight of 9 lbs. is easy to shoot well with.

I would suggest that Matt get one of his new strain screws out of stock and file fit it to produce a 9 lbs. trigger pull. Because the difference between 8 and 9 lbs is almost unnoticeable and a 9 lbs. trigger will function with 100% reliable ignition with Remington UMC ammunition. BTW, my experience is that recent Remington primers are about as hard as you will find but their cases are excellent for reloading with flash holes that don't need reaming for those of us cleaning with SS pins. Because of this when I need a new batch of Once Fired cases I shoot off one of those UMC megaboxes or buckets. So, I have re-tuned every one of my revolvers to a 9 lbs. trigger.

alec.mc · Aug 18, 2016

scooter123 said:
Doc, changing the REbound Spring has almost no effect on the weight of the Double Action trigger pull,

Completely false. Putting in a lighter rebound spring WILL lighten your double action pull. Though, you cannot go so light on the rebound that it doesnt have the strength to overcome the weight of the main spring to reset the trigger.

------------

OP, I find the problem with Wolffe main springs is the 'rib' where the strain screw sits is relived too far and you need an extra long strain screw. Try something like the Jerry M " Bang Inc " main spring, they are flat all the way up and very easy to adjust with your strain screw. I also think they work a ton better than a Wolfe main spring.

Also, if you are in a pinch at a match or something, you can " shim " the strainscrew by putting a piece of small metal, cardboard, whatever you having laying around in between the strain screw and main spring to give it more length / tension.

Best of luck.

series guy · Aug 18, 2016

A spent primer with the anvil removed makes a dandy strain screw shim. I tap the dent out with a small punch before using.

MichiganScott · Aug 18, 2016

Buy two new strain screws. Shorten the first one until it is just a bit longer than the one currently in the gun. The second one is a spare in case you over shorten the first.

For this weekend, place a tiny homemade leather washer under the strain screw. I suspect the original was over shortened.

Protocall_Design · Aug 18, 2016

I use #8-32 x 1/2" socket set screw (no head) with flat point. Install with blue Loctite. Then you can tune it to whatever you want and it will stay there until you turn it with the allen wrench. I will probably get flamed by the purists, but I have been doing that for years in my competition guns and never had a problem. Using the trigger pull gauge on the hammer, I can then make the hammer any weight I want by dialing the screw and checking the pull weight.

This type of mod is not recommended for carry guns.

lefty_jake · Aug 18, 2016

There are many threads about mainspring tension on this forum.

In your case, I would probably replace the strain screw with an 8-32 socket set screw as described by Tomcatt51 in post #22 of this thread:

http://smith-wessonforum.com/s-w-smithing/356297-625pc-hammer-weight-adjusting.html

That whole thread has lots of useful information, but it is also a huge thread, and many posts are focused on issues which are specific to the model 625.

I personally would not use a set screw to replace the strain screw on a duty gun. But I have used this method on range only guns, and the screws do not move at all if thread locker is used appropriately. I would trust this method for a competition gun, and it allows very precise and reversible adjustments.

Using a primer as a shim to extend the strain screw may also be a good solution in your case. This is an expedient method for a field repair, and it works well. However, the primer may be even thicker than you need. Turning the strain screw 1/8th turn, which extends its length by about .004, often makes a significant difference. These adjustments are quite sensitive.

Also, the following thread shows a method for measuring hammer spring weight that you may find useful. The method is shown in the attachment to post #2 that was generously provided by armorer951.

http://smith-wessonforum.com/s-w-smithing/441723-question-about-testing-hammer-spring-weight.html

matteekay · Aug 18, 2016

Thank you for the replies, all!

I posted that while I was still at the match last night (looooooong match, lol). Immediately after that COF I emptied, boxed, and marked all of the ammo on my belt and reloaded everything with American Eagle from different boxes. I ran the next two COF's without a single issue. It was surprising in the first place because American Eagle has never given me problems in hundreds of rounds fired previously.

Dr Denby said:
Just out of curiosity, have you tried different rebound spring weights?

In terms of the rebound spring, it's some kind of custom job and it's already very light. I dropped in the lightest one that Wolff sells and it increased the draw weight.

scooter123 said:
Good news is the installation of a Power Custom hammer nose completely solved the misfire problem and the original factory DA trigger pull weight of 9 lbs. is easy to shoot well with.

I'm really interested in the Power Custom hammer. Is it noticeably different from the stock one?

series guy said:
A spent primer with the anvil removed makes a dandy strain screw shim. I tap the dent out with a small punch before using.

Interesting! What do you mean by "anvil"?

Here are some photos of the gun as it sits - you can see that the mainspring isn't flexed all the way and the strain screw is at full-lock:

And here are the 4 light strikes I had:

In terms of what to do?

Well, I could leave it alone and hope that was a bad batch, lol.

I may try to shape my spare screw, but I'll probably drop the Wolff in there for the time being. Using the same strain screw, it adds exactly a pound based on my trigger pull gauge. It's going to be the quickest fix before the weekend.

matteekay · Aug 18, 2016

Toolguy said:
I use #8-32 x 1/2" socket set screw (no head) with flat point. Install with blue Loctite. Then you can tune it to whatever you want and it will stay there until you turn it with the allen wrench. I will probably get flamed by the purists, but I have been doing that for years in my competition guns and never had a problem. Using the trigger pull gauge on the hammer, I can then make the hammer any weight I want by dialing the screw and checking the pull weight.

This type of mod is not recommended for carry guns.

That's a great idea! Should let me dial it in exactly and adjust if I need to.

lefty_jake said:
There are many threads about mainspring tension on this forum.

In your case, I would probably replace the strain screw with an 8-32 socket set screw as described by Tomcatt51 in post #22 of this thread:

http://smith-wessonforum.com/s-w-smithing/356297-625pc-hammer-weight-adjusting.html

That whole thread has lots of useful information, but it is also a huge thread, and many posts are focused on issues which are specific to the model 625.

I personally would not use a set screw to replace the strain screw on a duty gun. But I have used this method on range only guns, and the screws do not move at all if thread locker is used appropriately. I would trust this method for a competition gun, and it allows very precise and reversible adjustments.

Using a primer as a shim to extend the strain screw may also be a good solution in your case. This is an expedient method for a field repair, and it works well. However, the primer may be even thicker than you need. Turning the strain screw 1/8th turn, which extends its length by about .004, often makes a significant difference. These adjustments are quite sensitive.

Also, the following thread shows a method for measuring hammer spring weight that you may find useful. The method is shown in the attachment to post #2 that was generously provided by armorer951.

http://smith-wessonforum.com/s-w-smithing/441723-question-about-testing-hammer-spring-weight.html

Awesome, thank you for the resources! Again, this might be the best solution. I'll probably give this a try tonight (as a hobbyist holster maker, I have LOTS of 8-32 screws, haha)

Lee's Landing Billy · Aug 18, 2016

I've never seen the spent primer trick NOT work. I've seen it a lot. It will actually give you a good bit of adjustment.

Steve912 · Aug 18, 2016

matteekay said:
Interesting! What do you mean by "anvil"?

The anvil is the little three-legged beastie you see, looking
into the open side of primer cup. It supports the primer compound against the cup and provides one side of the 'rock and a hard
place' when the firing pin dents the primer cup.

Those are some silly-light primer strikes!!

matteekay · Aug 18, 2016

Steve912 said:
Those are some silly-light primer strikes!!

Tell me about it. The baffling this is I've never had issues with Federal before and didn't after. I'm wondering if I maybe got a box assembled on Friday or something... I even played back my GoPro video and I definitely didn't short-stroke the pull.

I'll grab a few set screws and give it a shot.

ontargetagain · Aug 18, 2016

Since you mention that it happened all of sudden, perhaps there is a firing pin issue that has been overlooked?
I would be curious if these 4 would fire in single action or not, that would tell if you had bad primers perhaps?

In terms of rebound spring weight you say you have in the lightest and it has increased the pull tension, likely then the spring you had in was shortened or you are not feeling much tension at all on the rebound spring and immediately feeling the tension from the mainspring compression.
Just some thoughts, I am far from an expert but have certainly tinkered and learned

Karl

tomcatt51 · Aug 18, 2016

matteekay said:
Tell me about it. The baffling this is I've never had issues with Federal before and didn't after. I'm wondering if I maybe got a box assembled on Friday or something... I even played back my GoPro video and I definitely didn't short-stroke the pull.

I'll grab a few set screws and give it a shot.

Good idea. An 8-32 socket set screw works well (though it drives the forum purists nuts) and is easily adjustable. I use purple Loctite 222 (it's meant for small diameter fasteners you will be adjusting) on them or a bit of wicking Loctite 290 after adjustment.

You can also hand seat the primers in your factory ammo which might make a mainspring preload change unnecessary.

matteekay · Aug 18, 2016

ontargetagain said:
Since you mention that it happened all of sudden, perhaps there is a firing pin issue that has been overlooked?
I would be curious if these 4 would fire in single action or not, that would tell if you had bad primers perhaps?

Valid thought. This particular gun has a nosed hammer and I've often wondered if it's gotten worn in its 30-year life. If I can confirm that that Power Custom one is longer I'll probably pick one up.

I didn't have a chance to test it out in SA, unfortunately.

matteekay · Aug 18, 2016

tomcatt51 said:
You can also hand seat the primers in your factory ammo which might make a mainspring preload change unnecessary.

I've thought about this but it kinda terrifies me, haha.

scooter123 · Aug 18, 2016

alec.mc said:
Completely false. Putting in a lighter rebound spring WILL lighten your double action pull. Though, you cannot go so light on the rebound that it doesnt have the strength to overcome the weight of the main spring to reset the trigger.

I have a Lyman Digital trigger gage and have actually used it to MEASURE the effect of changing the weight of the Rebound Spring. It is insignificant, as in an ounce or two.

As for why this is the case, the rebound slide is operated by what is typically called a Toggle Link in Engineering. As the Toggle Link alignment approaches the line of the Force Vector the mechanical advantage of that link increases exponentially. So, as the trigger is acting on the DA Sear and acting in a vector near perpendicular to the moment arm for the hammer the as the mainspring is approaching it's peak in tension and the toggle link is nearly flat, so the net effect is almost no change in the force exerted on the trigger by selecting a lighter rebound spring. Now, what a lighter Rebound Spring can do is change the initial weight of the trigger pull in double action, so a lighter Rebound Spring can reduce the Initiating force but at that point the trigger pull is light enough (in the range of 3 or 4 lbs.) we really don't notice that.

tomcatt51 · Aug 18, 2016

matteekay said:
I've thought about this but it kinda terrifies me, haha.

Yes. but it takes an impact with considerable velocity to set off a primer. We PRESS them into primer pockets regularly when reloading. All my handgun reloads come off Dillon Square Deal B's. It gets them flush but not fully seated (fully seated being .008" to .010" below flush) so all my revolver ammo gets another step, fully seating its' primers by hand after the rds are loaded.

tomcatt51 · Aug 18, 2016

scooter123 said:
I have a Lyman Digital trigger gage and have actually used it to MEASURE the effect of changing the weight of the Rebound Spring. It is insignificant, as in an ounce or two.

Wow!!! I guess I've been deluded replacing factory rebound springs with 11 lb springs with 3 coils clipped.

Best way to raise mainspring tension?

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