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Discussion Starter · #1 ·
Been fooling with springs in an N-frame 325PD, including some mainsprings in my spares box.

There seems to be a difference in effort among them, tho' there is no readily discernible difference.
Are the flat S&W mainsprings different?
Thanks,
Moon
 

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Discussion Starter · #8 ·
Kar, that is indeed the creature. It is an answer to a question that no one asked, tho' it does make a great woods walker. It is rappy to shoot; several friends have them as well. I stumbled on this one LNIB, and I do like revos that use autopistol rounds.

Andy', several flat mainsprings in my stash have more arch than others, and I had an N that started experiencing misfires; its mainspring had taken a set.
Redcat, I could shoot .45 GAP in it; presuming they fit in the moonclips, but I can't think of a compelling reason to use them. I may reload some lighter stuff to give my hand a break. This gun is a pretty good inertial bullet puller.

Mike, I never fool with the strain screw. It does make a handy way to install the mainspring, but it's of no use for adjustments.
Eventually solved my own problem by putting a vernier on the mainsprings at the spot where the strain screw bears on them. Several were a couple thousandths thicker there. I put one of those in, and the misfires disappeared.
Thanks all,
Moon
 

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Discussion Starter · #9 ·
BTW, Mike, I was reading somewhere else that the strain screw can wear down in much-fired Smiths. I don't lend much credence to this; what do you think?
Moon
 

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Discussion Starter · #11 ·
Actually, PPS, it made a huge difference.
I'd pulled the original mainspring for a ribbed one, and the original went in among my spares.
The ribbed one didn't work at all, tho' the double action was great. The replacement, picked at random from the spares, felt about like the reduced power ribbed one.
Which is what sent me scurrying to the computer to ask, and back to the spares to start measuring.
There were two that were a couple thousandths thicker, and the difference with one of them, back in the gun, was surprising. The double action pull, or thumbing the hammer, was noticeably heavier. And all the cartridges went boom, including some factory stuff with harder primers.
After that long, windy explanation, my stash of (coil) rebound slide springs only vary by less than a thousandth as well.
Moon
 

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BTW, Mike, I was reading somewhere else that the strain screw can wear down in much-fired Smiths. I don't lend much credence to this; what do you think?
Moon
I dunno. But if it does, it would seem a simple matter to fix: tighten the screw slightly.

M

P.S. Leaf springs are by their very nature much harder to manufacture to a predictable and consistent strength than are coiled-wire compression springs. That's the reason for strain screws.
 

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The strain screw does not wear out but walk out, it is a common problem in heavily recoiling S&W revolvers. Not only the strain screw but also the front side plate screw that holds the crane and cylinder assembly in, is subject to being shot loose.

A friend with a S&W 625 found that out during a reload in a competition: the whole cylinder assembly fell out of the frame and got scratched. I had the same with it, even though I always tightened the sideplate screws regularly. Loctite is a way to insure against this, or shooting a Korth:).
 

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The strain screw does not wear out but walk out, it is a common problem in heavily recoiling S&W revolvers. Not only the strain screw but also the front side plate screw that holds the crane and cylinder assembly in, is subject to being shot loose.

A friend with a S&W 625 found that out during a reload in a competition: the whole cylinder assembly fell out of the frame and got scratched. I had the same with it, even though I always tightened the sideplate screws regularly. Loctite is a way to insure against this, or shooting a Korth:).
I have no experience (unfortunately) with Korth. I've found with the Smith's a little dab of loctite is a decent remedy and is probably more cost effective than switching to Korths.

(Just kidding Andy. I'm mostly a little jealous as I've never shot much less owned a Korth).
 

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...

P.S. Leaf springs are by their very nature much harder to manufacture to a predictable and consistent strength than are coiled-wire compression springs. That's the reason for strain screws.
Come to think of it, there is another reason.

Target shooters who anticipate shooting only under favorable conditions, using ammunition of known performance, can adjust the strain screw to give a very light and easy action that is just enough to give positive ignition, but no more. This doesn't leave much cushion for irregularities, but then it's not the life-or-death reliability that one should provide for self-defense.

M
 

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Discussion Starter · #16 ·
The advice, from a factory-trained S&W 'smith, was to not back off on the strain screw. He liked changing out springs (the rebound slide spring especially; it powers the trigger), and polishing things. I'll look back thru' my textbook to double check about the strain screw.

Clipping 1.5 coils off the rebound spring can be done, or order a kit from Brownells, which has a whole range of rebound springs, from 11 to 15 lbs.
I have miked individual wires, and several adjacent weights will share a thickness, so it must be the number of coils that effects the weight. Mike, I concur, making flat springs must be even worse than coils.

The ribbed, reduced power, mainspring was another route, which has worked extraordinarily well in other K,L, and N Smiths.
Just, in this case, it was too much of a good thing, or it is something peculiar to the geometry of the 325. It is frankly the only alloy framed N frame I've ever tinkered with, and one of the few that exist.


Two other issues with backing off the strain screw; it won't stay in adjustment if it is simply backed off; it has to be ground to length and then snugged against the grip frame. And, if you back it off too much, the mainspring will encounter the grip screw, or vise-versa.
Thanks,
Moon
 

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Halfmoonclip,

I agree on not backing out the main spring strain screw. A friend was a S&W certified armourer and CSI, also an accomplished PPC shooter, and he took two afternoons to show me how to work on my S&W revolvers when I moved to Florida. The Kuhnhausen manual also warns against overly cutting the strain screw to avoid buckling, which occurs when the spring isn't bent enough and therefore is too long. Factory rebound spring have 17 turns, Kuhnhausen warns against having less than 15.

I can recommend Kuhnhausen S&W Shop manual to anyone who wants to know how the S&W revolver works and can be improved.
 

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Discussion Starter · #19 ·
I have a loose-leaf factory manual that an armorer friend was kind enough to share with me, but the Kuhnhausen Manual sounds like a thing well worth having.
Thanks, guys.
Moon
 
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