What is a strain screw?

[halfmoonclip]

I had the mainspring go south on one of my Smiths; it's not common, but any spring can fatigue on not be made correctly. I had a number of mainsprings in my 325 alloy .45 too; they were all theoretically the same, but some would fire reliably and others not. There was a couple thousandths difference in thickness.
I would try calling Smith; their customer service is second to none. They may well send you a strain screw.
I wouldn't over-think any other issues the gun may have, if the action works smoothly and doesn't feel gummy.
Actually, Smith might even want you to send it in on their dime. They have treated me uncommon well.
Moon

[shadowrider]

When we used to carry revolvers on duty, one of the "great ideas" to reduce double action trigger pull was to loosen the strain screw. BAD IDEA!! It is not an adjustment screw, it is supposed to be tightened down all the way. When the armorer told certain officers to keep them tightened all the way, some closet gunsmiths decided to removed the mainspring, bend it near the top with a little kink in it, then re-install. This also reduced the double-action pull on the trigger. HOWEVER, this resulted in even more "light hits" on the primer, and misfires.
SO, if OP found his strain screw was cut to reduce the length, it is also possible the original spring was bent (purposely) to help reduce trigger pull by the same "gunsmith" that cut his screw. I have never seen an unaltered mainspring lose it's power and need to be replaced due to age. The original mainspring in my Model 66 (no dashes) is still good as new, as is the one in my model 15 (50 years old).

You can bend the factory spring some, but you have to know what you are doing. The better smiths in my area, well..when there were some around anyway, but they preferred to bend the factory spring over using an aftermarket. S&W springs usually don't wear out and always seem to have the best feel. You can bend them a little and you can get a little more weight off the trigger by reducing the rebound spring weight but the key is to NOT go nuts with either one. If you want a radically lightened DA trigger you have to chop the hammer to reduce it's weight. That gets the speed on the hammer back up where it has to be.

[halfmoonclip]

If you really want to take something off the mainspring, Brownells sells a ribbed mainspring (for K,L&N frames); it normally gives a lighter double action without causing misfires; the alloy 325 I mentioned above being the exception...didn't work at all.
If you want to fool with the rebound slide spring (trigger spring), Brownells will sell you a range, from 11lbs to 15, to allow experimenting with what works. 11 is usually too light, but 12 generally gives a nice trigger without letting the trigger hang up.
Moon

[ThirdWatcher]

When we used to carry revolvers on duty, one of the "great ideas" to reduce double action trigger pull was to loosen the strain screw. BAD IDEA!! It is not an adjustment screw, it is supposed to be tightened down all the way. When the armorer told certain officers to keep them tightened all the way, some closet gunsmiths decided to removed the mainspring, bend it near the top with a little kink in it, then re-install. This also reduced the double-action pull on the trigger. HOWEVER, this resulted in even more "light hits" on the primer, and misfires...

+1. As a rookie, I was told by more senior officers that I could get a better trigger pull by backing out the strain screw on my issued Model 28-2 but I knew better. My Dad gave me a new-used 28-2 when I got out of the Army and I took it to a gunsmith when I began having misfires. Turns out the strain screw was backed out. Reliability is much more important than a lighter trigger pull.

[Don Quijote]

Real good advice from everyone on this thread.

[halfmoonclip]

BTW, always wondered about the strain screw, and have finally concluded it wasn't meant to adjust anything, but rather as an aid to assembly. It would take one heck of a tool to compress the mainspring into place without it.
Moon

[JerDerv]

Good tips. Im a fan of the wolf brand main springs.