K-22 firing pin protrusion?

Short version:
How far should the firing pin protrude past he recoil shield on my '55 K-22, when the hammer is down in the fired position?

Longer version:
I've looked but haven't found a spec on how far the firing pin should protrude on my 1955 vintage K-22 with the frame mounted firing pin.

I don't think the firing pin is an issue but I'm getting some fail to fires with ammo that shoots 100% in other guns. Strain screw is tight, the spring hasn't been messed with. The strikes *look* deep enough but there's some reason for the high rate of FTF (50% with one particular ammo).

I'm thinking to replace the hammer spring. Maybe shim it up as a test.

The tip of the FP should come within a few .000 of touching the chamber rim recess,,but NOT actually touch it.

That will be more than enough to fire any decent quality ammo given a proper rounded firing pin profile 'point' AND a proper mainspring tension.

If the firing pin reaches and actually touches the chamber rim recess it will not give the hammer slap any more energy to the fall. But it can cause damage to the chamber rim recess and chamber itself by turning up a burr in the metal.

I sometimes check how far a RF firing pin extends into a chamber recess by placing a round paper punch-out in the chamber recess.
Carefully placed into the recess and then the gun 'dry-fired' (one of the few times I do that) to see if the firing pin tip reaches the paper sitting on the bottom of the recess.
Another way is to use a marker and ink up the rim recess. Then dry fire. Then examine closely. See if the FP is hitting the chamber at all.
This will tell you if the FP is too long or not.
It won't tell you if it's too short.
You can get a good reading on that on the revolver by using a simple feeler gauge to get the distance from the breech face to the cylinder face. Then a little carefull caliper or depth micrometer work to measure the rim recess.
Add them together for a max depth/length of protrusion of FP.
You know by the first test that the FP is not hitting the chamber so that full max depth is not being reached.

The mainspring strain screw can be turned in to it's limit, but it could be that the threaded end has at some point been shortened a small amt to give a lighter trigger pull in DA.
The other effect that can have is a lazy hammer fall with less energy behind it and misfires in both SA and DA.

Take a very close look at the tip of the strain screw and see if it looks like it's been filed or ground off a bit.
One trick to put them back in order if they have been is to use a spent CF primer,,take the old anvil out and place the cup of the primer over the end of the strain screw and against the main spring.
That small amt of thickness in that primer cup is often enough to bring the mainspring back to full strength when the screw is turned back in all the way.

It's always a good idea for old revolvers, to spray cleaner in the firing hole to flush out and eliminate old gunk that's making the firing pin sluggish.

Recognize that it's an inertia firing pin; it has to fling forward when hit by the hammer further than the hammer actually holds it forward when in the firing position. Gunk in the firing pin cavity will limit the forward travel from inertia.

You must push the back of the firing pin forward with a pin punch to verify how far forward it can actually reach.

A few questions.
One is this gun new to you? If yes you really don't know what might have been done as said above unseen gunk gumming up the firing pin, strain screw might be shortened.
If you have owned it for a long time, and it only recently started this then it may just be gunked up.
I can't imagine how many shots it would take to wear out a mainspring. I suppose it happens, but I doubt much.

Thought

Instead of paper or a magic marker, their is a cheap product at auto supplies called plasti gauge. It is like $5 at auto zone. It is some very thin strips of soft clay like plastic. You could easily place some it on recess ledge and dry fire. Comparing the width it is smashed to with a chart on the package and it would tell you just how close the firing pin came

But, I agree with the possible gunk in firing pin area.

Very nice, this all gives me something to work on. Hondo44 may be on to the culprit with gunk in the recess for the firing pin.

Merl67, Dad bought this revolver new and I've had possession of it for about 25 years. It doesn't get fired nearly enough but it has in the past.

It's ftf'd occasionally in the past and I've blamed the ammo. A recent batch has had a high FTF rate but only in the K-22.

I'm going to work on that firing pin recess tomorrow and see if I can get a handle on how far that firing pin is dropping. 2152HQ has given me some ideas on how to determine that.

Plastigauge ... of course, I've used it years back. I think I'm going to try feeler gauges, see if I can get an idea if there's a gap when the firing pin is fully forward. That would tell me right away there's a problem.

I'm leaning towards the firing pin recess ...

Thanks, guys.

There is a nit to pick here. The firing pin on a K22 is not an inertia firing pin. When the hammer strikes the firing pin, the hammer drives it to its maximum extension, not inertia. If the trigger is held back, the firing pin will remain protruding from the breech face.

After the trigger is released, the hammer rebound mechanism moves the hammer off the firing pin and the firing pin spring withdraws the firing pin from the cartridge rim.

Compare that to true inertia firing pins on Model 1911-pattern pistols, and most centerfire semi-automatics. When the hammer rests on the firing pin, which it does any time the hammer is at rest, the firing pin will not protrude from the breech face.

No need for anything fancy to test firing pin protrusion. Just use a dab of modeling clay.

I suspect a main spring issue. The mention of a shortened strain screw is a likely culprit if the main spring looks original, unless the firing pin channel is filled with gunk. I would also remove the main spring and see if the curve appears correct, because some bubba gunsmiths bend the main spring to lighten the trigger pull.

Check cylinder end-shake, too. If one or two chambers have end-shake, it can cause ftf, even when the other chambers work fine.

The primer hack fixed mine.

Not only the firing pin recess, but all of the interior may have a degree of gunk slowing down the hammer fall. Unless the gun is relatively new I would recommend a side plate removal and a good thorough leaning and lube.

steelslaver said:

Thought

Instead of paper or a magic marker, their is a cheap product at auto supplies called plasti gauge. It is like $5 at auto zone. It is some very thin strips of soft clay like plastic. You could easily place some it on recess ledge and dry fire. Comparing the width it is smashed to with a chart on the package and it would tell you just how close the firing pin came

But, I agree with the possible gunk in firing pin area.

Click to expand...

Never heard of the Plasti-Gauge stuff, sounds like usefull stuff. I'll have to pick some up.

The magic marker/paper gives you two things.
The magic marker tells you if the pin is too long and is stiking the chamber recess or edge. Usually seem easily enough w/o a marking coating applied but it helps to ID any problem.
A FP that is too something not really in the mix here I guess but easy to check while going over the gun.
.
The piece of paper fit into the rim recess lets you know if the FP is long enough.
If it imprints the paper,,,,then it's the right length.
The prior test showed that the pin wasn't too long in that it didn't contact the chamber rim recess itself.
The paper , common note paper is .005 thick (approx) and that is the clearance you want betw the tip of the RF FiringPin and the chamber.
I use the punch outs from a 3 ring binder punch (are they around anymore?).

I didn't explain it well at all and it's an old way of doing things.
I'll give the Plasti-Gauge stuff a tryout. It'll be handy for other parts fitting as well.
Thanks for the tip!

JudgeColt said:

There is a nit to pick here. The firing pin on a K22 is not an inertia firing pin. When the hammer strikes the firing pin, the hammer drives it to its maximum extension, not inertia. If the trigger is held back, the firing pin will remain protruding from the breech face.

After the trigger is released, the hammer rebound mechanism moves the hammer off the firing pin and the firing pin spring withdraws the firing pin from the cartridge rim.

Compare that to true inertia firing pins on Model 1911-pattern pistols, and most centerfire semi-automatics. When the hammer rests on the firing pin, which it does any time the hammer is at rest, the firing pin will not protrude from the breech face.

Click to expand...

If you're more comfortable with calling it a semi-inertia firing pin, be my guest. But if you don't think inertia is involved, you haven't learned how it works or actually proved it to yourself by testing it as described in my post. Because that will show you that by pushing it forward the pin will extend an additional .005" + or - forward from how far it protrudes when held by the hammer resting on it.

If you think; "When the hammer strikes the firing pin, the hammer drives it to its maximum extension, not inertia.", that would mean the pin return spring would have to be completely compressed and bound up and/or the firing pin wedges against its larger taper at its back end, and likely stick in the firing pin hole. A very poor engineering design!

For full skeptics, but be forewarned: rotate the cyl to align the forcing cone between two chambers and let the hammer fall. When you open the cyl you will observe a perfect round dent from the firing pin in the cyl face between the two chambers!

Ok, so here's where I'm at - I'm going to replace the spring and screw.

No plastigauge at my local parts store. I fiddled with paper, etc and just couldn't get a good read on firing pin protrusion, BUT I can confirm it's well past the rear face of the cylinder and has never bottomed out. So I think it's fine.

I cleaned the firing pin recess and I can hear a difference when the firing pin bottoms out so I know there was gunk in it. I pulled the sideplate and it was a little gunky inside. I took nothing out, hosed it with brake parts cleaner and let it dry. Oiled per multiple forum posts and the Midway revolver cleaning video.

Loaded up 6 rounds, sure I had solved my problem. 4 required a second strike. GrumbleGrumbleGrumble.

Back to the bench and I do the primer on the strain screw trick. 12 rounds later, zero failures to fire on the first strike.

When I get the new parts I'll take all the guts out and do a better cleaning. Meanwhile, I'll run another 50 or hundred rounds through it just to be sure.

Thanks for all the help.

Try removing the mainspring and straightening it out a bit. That sometimes will add just enough energy to solve the problem.

Sounds like you are well on the way to having it functioning correctly should be good for another 50 years, or so.

Hondo44 said:

It's always a good idea for old revolvers, to spray cleaner in the firing hole to flush out and eliminate old gunk that's making the firing pin sluggish.

Recognize that it's an inertia firing pin; it has to fling forward when hit by the hammer further than the hammer actually holds it forward when in the firing position. Gunk in the firing pin cavity will limit the forward travel from inertia.

You must push the back of the firing pin forward with a pin punch to verify how far forward it can actually reach.

Click to expand...

You said it all. Thanks.

I'm pretty certain this is the right spring:
Mainspring | Gun Parts Corp.

Anyone care to venture an opinion? I'll order it later today if nobody waves me off it.