Follow-up on poor ignition - Model 18.

max503 · Mar 13, 2025

I posted a while back about ignition problems my 1958 Model 18 was having. I tried reaming the cylinders and replacing the mainspring with a Wolff spring.
Neither of those fixes helped, so I ordered an extended-length strain screw from Wolff.
That didn't help.
Then I replaced the Wolff spring with the original 1958 spring and the extended length screw and Presto! No more misfires.
I've probably shot 500 rounds DA of various ammo and nary a miss-fire.
This gun only misfired when shooting DA.

Here's the original thread:
Still getting misfires with Model 18 after reaming

chief38 · Mar 21, 2025

Many shooters are unaware that .22 rimfire cartridges take more force to reliably set off than center fire primers do. Simply said, a 22RF trigger / hammer needs to be heavier than an equivalent center fire revolver.

stansdds · Mar 21, 2025

What Chief38 said is absolutely true. Rimfire cartridges are harder to reliably ignite than most centerfire primers. You cannot lighten the main spring significantly with a rimfire revolver and expect reliable ignition. S&W knew what they were doing when they designed their revolvers. It's the rest of us who think we have a better idea.

mogwan · Mar 24, 2025

Without taking my M18 out of the safe, I can't remember if the hammer held the firing pin or if it was a 'frame held' pin... Any possibility the firing pin (if hammer mounted) has just gotten peened or duller over the years?I knew firing pin for the hammer may help a lot. Don't remember if they made an extended pin if it's inset into the frame. It could also be an out of spec cylinder to flash shield measurement where the flat side of the .22 cartridges are no longer 'close enough' to the hammer when the hammer (or pin) engages the brass primer rim.

max503 · Mar 24, 2025

mogwan said:
Without taking my M18 out of the safe, I can't remember if the hammer held the firing pin or if it was a 'frame held' pin... Any possibility the firing pin (if hammer mounted) has just gotten peened or duller over the years?I knew firing pin for the hammer may help a lot. Don't remember if they made an extended pin if it's inset into the frame. It could also be an out of spec cylinder to flash shield measurement where the flat side of the .22 cartridges are no longer 'close enough' to the hammer when the hammer (or pin) engages the brass primer rim.

It has a frame-mounted firing pin. So far the extended strain screw has solved the problem 100%. If it acts up again I will look into gaps, headspace, and firing pin profile - and an OEM main spring. For now I am not going to borrow trouble.

Right now it has it's original (1958) mainspring and an extended strain screw from Wolff.

Follow-up on poor ignition - Model 18.

max503

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chief38

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stansdds

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mogwan

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max503

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