I have a problem with some ammo that has a harder primer rim (Winchester) and is very cheap ($7) and so many FF as to be hard to use even on range. The rounds generally fire the second hit and that indention is then deep as it is in CCI or Federals I have used.

What I am wondering is if I replace the mainspring with a new one from S&W will it solve this problem or will it continue? I would I guess replace the firing pin, and maybe FP spring, and bushing while I am ordering small parts from S&W.

But before I do this I was wondering if adjusting the tension screw would stiffen the mainspring some and maybe eliminate the problem? I have had a friend or two suggest I try backing off the screw a turn or two to see if that solves the problem. I had just assumed the screw was the way mainspring is held in place. So what say you guys, are my friends correct? Or do they just have a loose screw... most likely.

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Cranky Old Retired USN Guy

I have a problem with some ammo that has a harder primer rim (Winchester) and is very cheap ($7) and so many FF as to be hard to use even on range. The rounds generally fire the second hit and that indention is then deep as it is in CCI or Federals I have used.

What I am wondering is if I replace the mainspring with a new one from S&W will it solve this problem or will it continue? I would I guess replace the firing pin, and maybe FP spring, and bushing while I am ordering small parts from S&W.

But before I do this I was wondering if adjusting the tension screw would stiffen the mainspring some and maybe eliminate the problem? I have had a friend or two suggest I try backing off the screw a turn or two to see if that solves the problem. I had just assumed the screw was the way mainspring is held in place. So what say you guys, are my friends correct? Or do they just have a loose screw... most likely.

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Cranky Old Retired USN Guy

In my opinion, the strain screw should be screwed in fully tight and leave it there. Loosening it will only make the problem worse.

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Dick

I most likely should have asked if people had a problem with the cheap white box Winchester having hard primer rims and FF problems.

That said the first strike on fired and FF cases of this brand ammo are very faint but second hit really sinks in to rim.

I have always had them fully tight myself and really didn't think too much of the idea of loosing the screw.

But the urge to shoot the cheap dirty Winchester ammo is very strong because of price is only $7.25 a box and about the cheapest of other brands such as Federal or CCI is about $11 around here and that is a big price difference.

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Cranky Old Retired USN Guy

Dick's opinion is much MORE than just his opinion. It's an engineering FACT that S&W designed the spring tensin screw to be fully tight.

Your misfires can be due to other things than a mainspring tension screw that is backed out a bit. I would start by thoroughly cleaning under the extractor star, the rim seat counterbores, and the frame-mounted firing pin. Try dribbling a few drops of solvent into the hammer side of the firing pin, and manually pressing it a few times. The pin can get semi-seized up from dried oil. Check firing pin protrusion. The tip of the fp should stick out enough to crush the case rims, but not enough to impact the edge of the chamber. Lastly, check that cylinder endshake is not excessive, which can make the headspace excessive, and therefore reduce firing pin impact.

The gun was just returned from S&W and checked fine by them and as I mentioned it only happens with one brand of ammo and S&W even said that Winchester has a harder rim then most other ammo brands. They didn't seem to think the gun had a problem since it was just one brand the gun had a problem with.

Also I am very much the cleaning machine when it comes to cleaning my guns. I always clean under the extractor and oil the FP with Breakfree CLP on regular basis. The pin comes through just fine when fired (just hold cylinder release back to operate the trigger to watch come out) and actually thought it might be flattened some but close inspection pin is normal shape.

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Cranky Old Retired USN Guy

I have had 3 M-48's and while they have been a little finicky about ammo and accuracy I have never had one misfire with any of them with any brand of ammo.