I'm not much of a gunsmith, but my model 34-1 misfires every once in a while. I thought it might be the ammunition but that doesn't seem to make a difference. Just curious if it might be a coil mainspring. Everything else looks fine.
Any ideas would be appreciated. Thanks

I had an I-frame Kit that did the same thing. I replaced the original mainspring with a stock-rated one but the occasional misfires continued. Never did figure it out--no end shake, no obvious reasons for it--but I think it was ammo-related. Gave it to my daughter for a plinker/trainer with the info that it was not 100% reliable. She does not seem to have much trouble with it.

If changing ammo doesn't help I would consider sending it into S&W. They have solved a couple of gun mysteries for me over the years, as they seem to know a few things I don't.

Try the mainspring replacement first because it is a cheap easy fix. If that does not work, check the end play closely - the rimfires are very sensitive to excess end play. Also take a close look at the firing pin for damage.

__________________
Martin Co,FLA(finally made it)

Another item to check:

Make sure the hammer block safety is functioning properly; it's inside, between the hammer and the frame

When You pull the hammer back, it should be headed downward, and return upward as the hammer returns to forward position.

Make sure your shells are being fully chambered with the case rim
firmly seated against the cylinder. Dirty chambers can lead to misfiring
due to cushioning of the firing pin blow.

Of the S&W Kit Guns the M34-1 variation seems prone to this problem.
Several years ago bought a new one and experienced the same misfires. had my one gunsmith look at it and he said that I needed to use Winchester Ammo...no change. He could make it work in the shop with Winchester ammo, but at a 45 degree angle into his barrel. Worked great. At a 90 degree hold the problem came back with every type of ammo on the market. Paid to have the mainspring replaced with a factory replacement and then a Wolf spring and there was no change. Gave up and traded it off. Didn't even try try Customer Service.
That was almost the end of my association with S&W, but luckily sanity prevailed.
No problems with a M34 or Pre 34 only with the M34-1.
Never owned another one and never had another problem with a kit gun after that.
Thom Braxton
SWCA #1474

My 34-1 had a simular problem like yours and a PowerCustom endshake shim solved the issue. I know you said it had the correct amount of play, but even a tiny bit will cause misires occasionally.
The only drawback is PC does not make one fore a rimfire J-frame. The centerfire J's are a different dimension. The K will work, but the dia has to be reduced a bit.

Get rid of it! You don't want a dangerous gun like that around the house. I send you a $50 Walmart gift card for it.