How to determine if M15 mainspring should be replaces???

J

jrothWA

New member
Is there a measureable difference between FP depth on fired cases, to determined if the mainspring should be replace?

Go with S&W replacement spring or use the Wolff standard the offer , that is a couple pound force heavier??

Bought mine [in mid-90's police trade-in] used and MAY need to replace.

Thoughts.
 
Chances are you will never have to replace the main spring. If you are still getting good ignition it's fine. If you start getting light hits where the cartridge doesn't go off check that the strain screw is all the way in.

I've never had the need for a heavier mainspring.
 
There is no way to tell from primer strikes unless all strikes on all brands of ammunition are consistent.
The advice given you above is correct. I have never in 45 years had to replace a S&W "K" mainspring unless someone had been grinding on it.
 
I've only HAD to replace one S&W mainspring, that on my circa 1920 I-frame Regulation Police.

I picked the gun up one day some years ago and it rattled. I pulled the grips and found that the mainspring had broken right at the point where the strain screw bore on it.

Odd, but easily fixed.


That said, I have replaced most of the mainsprings on my S&W revolvers with Wolfe Power Rib springs.
 
"...MAY need to replace..." Not for any mechanical reason other than damage. Main springs usually only need replacing for a trigger job. Springs do not lose temper from being compressed.
 
I only replace two of them, both were on New to me used guns where the original owner had done some modification. One was bent to lighten the trigger pull, the other on a 25-2 was ground to about 1/2 original width. Light strikes were the result of both modifications.
 
I would suggest that you disassemble and thoroughly clean the internals of your S&W then lube it before replacing the mainspring.
 
Whoa there big fella.

Before you take the entire gun apart, make sure the strain screw is screwed in all the way. Lots of guys back it out a bit to lessen the force of the spring. The strain screw is supposed to be screwed in all the way. Backing it out can result in unreliable ignition.
 
Seven High said:
I would suggest that you disassemble and thoroughly clean the internals of your S&W then lube it before replacing the mainspring.
Driftwood Johnson said:
Whoa there big fella... Before you take the entire gun apart, make sure the strain screw is screwed in all the way.
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+1. Suggesting a complete teardown is like suggesting an engine rebuild in order to fix a rough idle, without changing the spark plugs and cleaning the throttle body first!

The #1 cause of light strikes on a S&W is a loose strain screw. #2 is a strain screw that has been filed down by an ill-informed former owner. A distant #3 is that an aftermarket low-power mainspring has been installed—or the factory mainspring has been bent—again by an ill-informed former owner.

Fixing #1 is cake. #2 is only slightly more complicated. #3 gets a bit more involved but is still reasonable.

OTOH taking the lockwork apart is on another level of difficulty entirely, and should NOT be attempted unless one is comfortable handling intricate parts, has some basic gunsmithing tools, AND has a good tutorial available on how to put everything back together properly.
 
"Suggesting a complete teardown is like suggesting an engine rebuild in order to fix a rough idle"

No. Not even close.

Many S&W revolvers I've encountered over the years could benefit a lot of a full tear down and thorough cleaning.

At worst, you get an close look at the operational parts of your gun. You're not rebuilding it, though, when you put all of the original parts back where you found them.

Regarding the "good tutorial," any NRA Exploded View disassembly instruction is MORE than adequate to the task. There are also a plethora of Utoob videos available on the subject, but granted, they range from pretty excellent all the way to "give that guy a chocolate gun, it's all he should be messing with."
 
OK, mebbe my analogy was a bit extreme. :)

Detail stripping these guns is NOT a nightmare, but I'd argue that it's not exactly simple either.

I've only ever bought one Smith new (which I've since sold), and of all of the used Smiths I've owned, only one has really required a complete teardown and cleaning to function well—and I believe this was caused by years of OVER-lubrication with a substance that subsequently dried up. (The lockwork was coated in sticky oily glop with the feel of dried maple syrup, and the trigger pull felt like the hammer was being dragged through mud. :()

I just don't want jrothWA to come back here and report that his cylinder now advances only when the barrel is pointed at the floor (lost or incorrectly installed hand spring). :rolleyes: This should be a really simple fix.
 
, make sure the strain screw is screwed in all the way.
Click to expand...

OK, now this has me wondering...WHAT IS THE PROPER / CORRECT POSITION FOR THE STRAIN SCREW????


I have always believed that the correct depth was with the screw head FLUSH WITH THE FRAME. Neither above, nor below. Unfired, (un worked on by owner) factory fresh S&Ws I have seen have the strain screw head flush with the frame.

With every S&W I've ever had (19s, 66, 27, 28, 29, etc.) "screwed all the way in" means the screw head is BELOW flush with the frame.

SO, what is correct???
 
Not really a position.

Snugged down tight in the screw seat is correct.

Don't worry about it protruding, or being recessed, or flush. Just make sure that it's down tight.
 
OP: One trick that you can try is to place a spent primer between the strain screw tip and the mainspring. This should increase the mainsprings strength somewhat.
 
Just bottomed out & tightened up tight.
Where the screw head rides is irrelevant, it's the OTHER end of the screw you worry about. :)
Denis
 
I have bought well over a dozen of used S&W revolvers and found many of them having greatly profited from a good cleaning of the action. I also inspect all parts and polish moving parts, if necessary, judging from wear marks.

Many guns had the mainspring pressure lightened by filing the strain screw down, or the mainspring bent, and having the rebound slide spring cut, so some diligence is in place when a simple function test fails.
 
Please permit me some disagreement with part of the above. IMHO and experience, the number one cause of problems with handguns (as brought to a gunsmith) is the owner taking the gun apart and either 1) messing something up or 2) being unable to reassemble the gun correctly (and maybe messing something up trying).

Jim

P.S. Yes, "messing something up" includes losing parts!

JK
 
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