Would this be fixed by installing a set of Wolfe main and rebound springs? If not, what else should be done? The strain screw is all the way in.
The gun is over 45 years old.

Pistol primers maybe???

It is an S&W K frame 22 rimfire revolver. The firing pin leaves very light dents in the rims. Lately it averages about 1 misfire per 12-20 shots. The rounds alway go off on the second blow.

I put some Wolfe springs in my GP100. It was to lighten the trigger pull. What a waste of money. It misfired half the time. I put the original springs back and have had no problems. If you get a spring kit make sure it's a heavy one.

If a new mainspring does not help check your headspace and firing pin protrusion.

Also make sure all the action parts are clean and lubed. Things can get really gummed up if not disassembled and cleaned periodically.

The strain screw should always be screwed in tight. Getting new springs is a good idea. Keep the old ones in order to put it back to original.
Take a look at the firing pin and make sure it's in good condition. I'd check the headspace too , to make sure the case rim isn't too far away from the firing pin. Make sure your cylinders are clean so the rounds fully chamber and are supported solid. Clean under the extractor star too. Try all this and let us know.

Joe

A lot can happen to a mainspring in 45 years. The can get weak and they can be tinkered with. Some folks have the notion that backing the tension screw out will give a lighter trigger pull. It will, but it can cause misfires. I had one that was a real head scratcher until I discovered that the tension screw had been shortened by some well meaning individual. A new spring and strain screw solved the problems.

The Wolfe spring kit may do the trick. Also check the length of the strain screw to another if you have one. If the new mainspring doesn't solve the problem, replace the strain screw.

The rebound spring has nothing to do with the misfiring but you might like the feel of the trigger with a lighter one. You'll know the rebound spring is too light if the trigger will not reliably return to the forward position.

I just pulled a K22 rimfire out of storage last night.

I am looking at it now. The firing pin is separate from the hammer.

There are three possibilities I can see:
1) Weak hammer spring
2) Firing pin too short
3) Crud blocking the firing pin from going forward

As an experiment, I would put a fired 22 case in one of the chambers with a virgin part of the rim at top dead center. I would pull the hammer back and cock it. Then I would reach around the hammer with a punch and claw hammer and hit the back of the firing pin. I would then compare the mark left on the case to the other light strikes.

If it is still light, you have firing pin problem. If it is a good hit, you have a spring problem.

Or you could just pull back the hammer and notice if it is too easy

Mine is about 7 pounds force straight down at the back of the hammer. I would use force gauge, but there is a scope on my revolver. I did calibrate my thumb to one hammer force, and then appy it to the force gauge.