mainspring aka strain screw adjustment?

[oldtater]

On my 1930 I frame .22/32 Heavy Frame Target in .22LR, can the strain screw be backed out a little to adjust the tension on the trigger action, or simply remain as tight/far in as it will go? Just wondered if the screw was meant to be used for slight adjustment. Many Thanks! OT

 

[Wiregrassguy]

The strain screw is designed to be fully tightened.

 

[Outpost75]

Also inspect and measure the strain screw to be sure that Bubba did not shorten it!

 

[Thaddeus Beauregard]

As stated, the strain screw isn't meant to be adjusted for DA pull weight fine tuning; it's meant to be fully tightened against the screw head. It can be adjusted and people do that often, but to do it properly, you would need to very carefully shorten or lengthen the screw and still tighten it completely so it won't work loose over time, impacting reliability. .22 rimfire revolvers are especially sensitive to dropping the spring weight. Another common practice is to replace the strain screw with a headless set screw and Loctite, but I wouldn't do that with any gun you would ever potentially use for self-defense.

 

[Dump1567]

You probably don't want to mess with the strain screw on a .22 due to reliability issues. If you want to lighten the pull, it's probably best to try different rebound springs (13, 14, or 15). The goal is positive trigger return when replacing the rebound spring.

 

[DARE]

Why is there an adjustment if you are not supposed to adjust it? Have found with my guns that if you back it off too much you can get some light hammer strikes resulting in misfires. The double action definitely gets lighter if you back off the screw. I think back it off some to get a good double action. As long as you don't have misfires, how is this a bad thing?

 

[robertrwalsh]

A lot of people are unaware that the .22lr rimfire needs MORE energy than (not less than) centerfire cartridges for reliable ignition. The hammer needs to hit fairly hard to do it's job. If you want to tweak it get a duplicate screw, shorten it bit by bit until you get unreliable ignition, then make sure the "real" one is a bit longer. Also .22lr ammo is a lot more variable than one might think. It might work great with Brand A but not worth a hoot with Brand B.

 

[Thaddeus Beauregard]

Why is there an adjustment if you are not supposed to adjust it? Have found with my guns that if you back it off too much you can get some light hammer strikes resulting in misfires. The double action definitely gets lighter if you back off the screw. I think back it off some to get a good double action. As long as you don't have misfires, how is this a bad thing?

Because it isn't designed as an "adjustment." The screw needs some thread length to span the gap between grip frame and spring and load up the spring and then be able to be backed out when needed so the spring can be removed. Since the spring flexes, it needs some screw length to put the spring in compression after initial contact. It has a head on it because it wasn't intended as an adjustable screw; otherwise a set screw would be used.

It's not necessarily a bad thing to back off on the screw as long as it's still 100% reliable afterwards, and people do it often. A lot depends on whether it's a range toy or a serious dedicated SD carry gun. For the latter, it's an unwise tradeoff to create a potential misfire for a slightly better DA trigger. The other issue is the fact that if the screw isn't shouldered tightly against the head, it can work itself loose over time and then you eventually get misfires unknowingly. In that regard, if you wish to reduce the pull weight, it's better to shorten the screw slightly than back it out or replace with a set screw and Locktite.

 

[DARE]

My carry gun is a Glock 23. Occasionally carry a Model 37. The Model 37 does not have a strain screw. Has the coil mainspring. When did S&W do away with the strain screw? Or do they still use it on some models?
My others are only used at the range, so a misfire not a problem. Going to back off all my screws where not happy with the double action.
Thanks for this thread for bringing this to my attention.

 

[Thaddeus Beauregard]

My carry gun is a Glock 23. Occasionally carry a Model 37. The Model 37 does not have a strain screw. Has the coil mainspring. When did S&W do away with the strain screw? Or do they still use it on some models?
My others are only used at the range, so a misfire not a problem. Going to back off all my screws where not happy with the double action.
Thanks for this thread for bringing this to my attention.

S&W did not do away with the strain screw. Most of their revolvers have a leaf spring and strain screw rather than coil mainspring. The J frame guns like your M37 have a coil mainspring because they need the extra power in a shorter envelope, acting on a smaller, lighter hammer in order to get ignition reliability. All J frame revolvers have the coil spring and every larger frame from K on up uses a leaf spring and strain screw.

 

[USBP SW]

The strain screw also gives the mainspring the proper arch to function as intended. Several years ago I purchased a 3" model 657 , it was listed as "non functioning", $250, I saw that the strain screw was backed out, I happily paid for the revolver and started my 10 day wait. When it was time to pick it up, I brought my S&W sight adjustment screwdriver, tightened the strain screw and the revolver functioned flawlessly. Personally, I would not alter the original equipment, it was engineered that way for a reason, if you want to improve the action, I would buy an aftermarket, lighter weight mainspring, then you can always change it back.

 

[DARE]

Well, I decided not to back them out after all. With target grips you have to take the grips off to get at the screw. On my .44 Magnum, when I backed the screw out a turn could not get the grips back on.
I never bought in to the screw just being there so you could remove the mainspring. If so, it is certainly an inelegant design.
If you can't back the screw out without modifying the grips, perhaps S&W thought you should not do it.

 

[Muley Gil]

Well, I decided not to back them out after all. With target grips you have to take the grips off to get at the screw. On my .44 Magnum, when I backed the screw out a turn could not get the grips back on.
I never bought in to the screw just being there so you could remove the mainspring. If so, it is certainly an inelegant design.
If you can't back the screw out without modifying the grips, perhaps S&W thought you should not do it.

How would you do it differently, if you were to redesign the S&W revolvers, knowing that this mainspring arrangement dates to the 19th Century??

 

[Thaddeus Beauregard]

I never bought in to the screw just being there so you could remove the mainspring. If so, it is certainly an inelegant design.

That wasn't the whole reason. The screw has to have some travel distance after making contact with the mainspring to compress it and generate the arc sweep needed for it to function properly. Also since the grip frame is the only place where you could put threads for the screw and because there is a gap between the grip frame and the spring, a long screw is needed to bridge that gap and apply compressive force at just the right location on the spring to flex correctly. S&W also did intend for the screw to be able to be modified for length if needed; it just didn't intend for it to be inifinitely user-adjustable. The screw head and the screw hole counterbore needs to make firm contact so the screw won't work loose and change spring compression during use.

 

[JwesleyN]

On my 1930 I frame .22/32 Heavy Frame Target in .22LR, can the strain screw be backed out a little to adjust the tension on the trigger action, or simply remain as tight/far in as it will go? Just wondered if the screw was meant to be used for slight adjustment. Many Thanks! OT

You can back it out until you get light primer strikes and some rounds not firing. Then move it one quarter of a turn and try it again until you get positive ignition and good firing pin strikes on double action. .22s depending on the brand you may get a dud once in a while.

 

[glowe]

I agree that these screws are not adjustment screws, except for maybe original adjustments made during assembly at the factory. Have never found documentation on how the factory set trigger pull, but often notice that these screws are not the same length in many of my guns. The original screws pre-WWII all had a smaller turned down section at the end of the screw and the length of that part of the screw is different from gun to gun. If the factory tested assembled guns with a gauge to get consistent trigger pulls, the easiest thing to do to change that pull would be to shorten the screw if the trigger pull was too high. Only other option would have been to disassemble the gun to adjust the internal springs. Anyone have any information on trigger pull adjustment at the factory pre-WWII?

 

[Eddie Southgate]

To me , backing the screw out much makes the trigger pull feel mushy and can cause the double action to tie up if you shoot it fast . As already stated it is not an adjustment but a means to correctly tension the spring after it is installed .

 

[steelslaver]

I know from my youth that a main spring screw that isn't tight will eventually work out and cause miss fires. How do I know this? Tried it and experience it of course.

I have become a big believer in smooth beats light and it is far better to be a great trigger puller than have a great trigger. None of which means I want heavy trigger pulls. Once everything is smooth, then try some trigger return springs, but always error on the side of a positive trigger return. Then take a bunch of ammo to the range and back the screw out a couple turns and fire it. IF every round fires turn it out another 1/2 turn and try it. Find out where it fails, then add 1/2 turn. The fire about 30 rounds. If there is even 1 misfire take another 1/2 turn and fire another 30 or so. When it never ever misfires, turn the screw back in tight counting every 1/2 turn it takes to be real tight. The screw is a 32 to the inch screw so every 1/2 turn moves the tip in .015625". Lets say your at 4 1/2 turns that is 4x.015625 or .0625". Measure the screws length then subtract .06 and file off that .06. and reinstall it dead tight. Now it should be reliable with that ammo, BUT, some primers are harder that others, some case rims are a little thinner than others, some guns have more head space than others and one with maximum headspace allows the rounds to move back and forth more in chambers. A round that is all the way back will absorb some of the hammer's energy as it is driven forward and be less likely to fire than one where all the hammers energy is applied to a primer in a case head tighter to the rear of chamber.

In other words if it positively has to go bang to save you or your loved ones tush, you need a very positive hammer blow, but if your punching paper a click will only be frustrating or cost a trophy.