Diagnose S&W revolver rimfire misfires

[LIProgun]

I was asked to look at a S&W 18-3 with a misfire problem and so far have come up empty.

The gun is in excellent condition, showing little use. When shooting double action, it will typically misfire 2 or 3 out of six chambers with .22 LR standard and HV ammo. Interestingly, all 6 chambers typically fire with the longer, CCI Stinger hyper-v ammo. All chambers typically fire single action, regardless of ammo.

Misfired cases show a noticable indentation, and may fire on a second hit if the DA trigger is worked very quickly. Staging the DA trigger slowly is almost certain to get misfires in most chambers.

A visual inspection turned up nothing. The gun was given a thorough cleaning, including the chambers. After cleaning, the chambers were lubed but then wiped as dry as possible.

The mainspring was replaced with a like-new factory S&W spring taken from a .357 mag K-frame. I am assuming the spring weight is the same on all K-frames, and that .22 revolvers don't come from the factory with a heavier spring.

After the above actions, the problem still persists.

Before I ship this out to S&W for service, I'd appreciate any advice.

 

[Dfariswheel]

There is a possibility that the firing pin is too short, due to damage/wear. Once saw one the owner had damaged, then just reshaped the end so he could sell it to the unsuspecting. The firing pin channel may be compacted with dirt/rust, or had the wrong pin/spring installed.

The action may be out of adjustment, slowing the hammer fall. Usually the first thing I look for in these cases is a weak/altered spring.

Use a punch to push the firing pin forward and see if it seems to be long enough or 'gummed' up.

let us know what you find.

 

[James K]

I agree that the firing pin is the chief suspect. A squirt of something like G96 Gun Treatment might clean things up. If it doesn't, and unless you are pretty expert in working on those revolvers, ship it back to S&W. I have seen many of those guns scarred up badly by attempts to get the firing pin out.

Jim

 

[Dfariswheel]

Just got back from lunch:

Another possibility:

A defective/wrong mainspring strain screw. Before the availabilty of spring kits, better 'smiths shortened the strain screw. (Less better 'smiths ground the mainspring).
If the screw was worked, it might be too short, lessening the mainspring tension.

I once saw a square butt 'K frame screw replaced with a ROUND BUTT screw, which is way too short.

Some people think that the strain screw is how you adjust the trigger pull weight. Nope, the screw must be down tight.

Compare the strain screw to one you know is unaltered.

STRONGLY second Jim, although the pin looks easy to remove, many S&W's and Colt's with frame mounted pins get damaged by the unwary. Better back to S&W.

 

[sw627pc]

Don't know about modern K-22's. But the old five screw guns (I have two) don't use the same mainspring as the rest of the K frame line. Don't know about the weight, but it is a different length (slightly) and putting a K frame spring in didn't work right.

 

[LIProgun]

Thanks to all. A few replies. The firing pin and channel were examined and *thorougly* cleaned. No gunk in there. The nose does not *look* damaged, but it could be worn. As I say, single action fires every round, so I am less likely to suspect the firing pin -- though I did consider it, and still will consider it a potential problem.

The strain screw appears full length and unaltered. A weak spring (or backed-off strain screw) were my first suspects.

I will heed the advice of removing the firing pin. Although I've worked plenty of centerfire Smiths, I have not worked on a rimfire Smith revolver before.

Again, thanks for all the helpful input.

 

[Master Blaster]

Another idea, Did you try going around the cylinder recesses with a dental pick or a Bamboo skewer?
There may be some crud caked into the the cylinder recess, this would cushion the blow of the firing pin on the rim of the cartridge. I had a misfire problem with all of my .22 revos, using target grade ammo, cleaning the cylinder helped
the tight fit, cleaning the recess that the rim of the cartridge rests on cured it. You really have to use a sharp pick of somekind to scrape the caked fouling off.
I thought mine were clean until I took a bamboo skewer to them, they all had caked crud here.

 

[BBBBill]

Headspace?

Endshake?

Firing Pin Protrusion?

Springs?

That's about all it could be.