Hey folks,

A bit ago I found a used but not abused Pre 18 at a LGS. I found it to be a bit unreliable, requiring double hits to light off various rounds.

Tips and suggestions from here led me to buy the Kuhnhausen manuals and dig in. I found the mainspring to be oddly bent and the trigger pull to be low, but smooth.

I’ve replaced the mainspring with a full power one. I’ve replaced and attempted to adjust the hammer weight as per the reading. I also did a serious detail clean and light re-lube.

Today I took a variety of CCI ammo to the range today to check my work. Results?

Single action ignition was great. 50-70 rounds shot single action without a hitch.

Double action, not so much. Every 6 round cylinder would miss 1 or 2 rounds. They would ignite on the second whack.

I did notice if I REALLY smacked it, FAST double action, the performance was better, but still not 100%.

So, what do the experts think? Do I need to go up some, lengthen, the strain screw? I’ve never found a definitive hammer weight for a K Frame 22LR, I set it to the weight for 357.

Any thoughts or tips would be appreciated!

I don't have a definitive weight for the hammer tension on a .22 K-frame, but I know that it's more than a centerfire. I've been able to get reliable ignition down to 38-40 ounces on a centerfire but all of my .22's require 50+ (they vary).

If it was mine, I would start with some basic checks of endshake, rear gauge (headspace), firing pin protrusion, and verify that the hammer is striking the firing pin without dragging on anything....then go to increased spring tension. An easy way is to take just the cup from a spent primer (remove the anvil and use a punch to flatten out the firing pin indentation) and place it on the end of the strain screw. Effectively you would be placing a shim between the strain screw and the spring. Going from memory, that should add .012" to .018" to the screw length, or about half a turn. If that improves the function then you know you need a longer screw. Buy several, they're cheap.

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SWCA #3942 / SWHF #988

You say you replaced the mainspring with a "full power" spring. Was it a S&W factory spring, or a Wolff "Power Rib" spring? Wolff springs require a longer than standard strain screw because the screw seats into the groove in the spring, but they don't tell you that!

Did you check end-shake per Kuhnhausen, or just worry about hammer energy?

Unless the hammer is binding in the frame for some reason there should be no problem if the hammer lift weight is what Kuhnhausen says it should be, and there is no excessive end-shake resulting in excess head-space.

Try putting the hammer only in the frame and install the sideplate with the screws. Then check to see if the hammer is completely free to move full travel.

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Gunsmithing since 1961

Check to make SURE the strain screw has not been ground down to where it is too short! No matter what brand main spring you install, a proper length strain screw will exert more pressure and cause greater force on the primer strike. If it has been ground down, (easy to tell by looking at the nose of the screw) buy a few and fit them to the proper working length. An unaltered strain screw will usually be rounded on the front contact point where a ground down one will usually be flat and missing the bluing.

NOTE: Always make the screw the proper length! Never loosen it and leave it untightened as it is not a variable adjustment and could eventually back out if not tightened properly. Rimfire ignition usually requires more force than center fire primers.

To answer a posed question, the replacement was a S&W flat spring, not a Wolff.

End shake and head space checked out. Good suggestion to verify the hammer is not dragging. I’ll do that.

I never found/saw a specific hammer weight given for the Rimfire, only the 38 and 357. I fit the screw to achieve the 357 weight. (I forget the number right now.). I have additional screws, so I’ll try the primer shim trick and see how that does. Sticking with CCI ammo for now as my control.

I suspect the strain screw to be shortened.

Strain screw length for sq. butt is .605" OAL and .480" under the head and rd. butt is .505" OAL and .380" under the head. You are welcome.

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Stang1911

Isn’t the strain screw supposed to be fit to the proper length to achieve the hammer hang weight specified?

Yes. To be technically correct, that's how it would be done. This method takes into account all the variables in screw length, spring bend or straightness and frame counterbore depth.
The biggest variable is bend in the mainspring, which can be easily adjusted to be more bent or more straight. Most times when the primer shim is used, the spring could simply be straightened a bit to achieve the same thing.

In practice, most people assume that all springs, all frames, and all screws are exactly alike, and you get a spring and a screw and screw it till it bottoms out and it's always exactly the same spring tension. This is far from reality.

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protocalldesign.com

I have owned 22 DA revolvers by Smith, Colt, Ruger, Charter, High Standard, and Taurus. None were 100% reliable on double action. Smith is better than most but not perfect.

Many of the problems with rimfire reliability stem from the accumulation of shooting debris, and gauge in the cylinder assembly, yoke and extractor.

Rimfire ammo is notorious for leaving behind an assortment of un-burned powder and bullet lubricants that have a "waxy", sticky consistency. This, coupled with the regular dirt, shooting debris, and less than nominal "regular" cleaning, often results in misfires and other anomalies.

Regular, thorough cleaning is a must, along with keeping the gun in spec, to the degree that is humanly possible. Using high quality ammo is also helpful.


Carter

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Ret. LE, FA Instr, S&W Armorer

Ok, I had an Un modified strain screw from Wolf. I measured the hammer weight as the revolver was - 5 samples, averaged 53 Oz. This is a fitted screw, as I’m the one who whittled on it. I replaced this with a new screw, and now the hammer weight measures 55 Oz over 5 samples. DA trigger pull moved from 125 Oz to 129 Oz (5 samples).

I’ll try to get to the range and see if this improves DA ignition reliability.

Updates soon.

Ok, it improved, but still mis-fires on 1-2 chambers per loading. It’s a little better in single action, but still misses.

At the range today, I cut a sliver from a 22 LR piece of brass and tightened it between the strain screw and the spring. This improved things, but still not 100%. This was with CCI mini-mags and Winchester Super X.

Do I just need to accept this is as good as it gets with a 1955 vintage revolver?

Should I try to remove the firing pin and spring and clean that up. (The Kuhnhausen book I have does not detail this disassembly. Any tips?)

Does anyone know the proper firing pin protrusion dimension for a Rimfire? Maybe it’s a tad short?

Extraction is not stiff, should I consider reaming?

Oh, the mis fires are NOT attributed to one specific chamber.

Anywho, still working on it!

All mine shoot 100% using double action......Iffen they didn't I'd fix em.

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S&W Accumulator

I had DA misfires with both a model 43 and a pre 18. I used spray brake clean with the narrow tube that comes with some aerosols and used that to flush out the firing pin space using a punch to hold the firing pin full to the rear and then full to the front while spraying. In both cases it fixed the DA misfires. Just something to try.

Stu

Go to an Ace hardware that sells gun screw and get an 8/32 screw with the right head. Grind it down until it is about 1/10" or so longer than the one you now have. Install it tight, and try it, then back it off 1/2 a turn try it and repeat until you get misfires. Then turn it back in 1/4 turn at a time, until you get none. Once you get none, turn the screw back in all the way tight counting the number of 1/4 turns until tight. Take that number of 1/4 turns times .078, remove the screw and remove that much from tip of screw, then reinstall it tight. Better to leave it a tiny bit long than be a bit short. You can get inexpensive digital calipers all over the place now. Everyone should have one.

It is my belief that smooth beats light and that being a good trigger puller beats having a light trigger pull

The main spring strain screw should be installed as is. Not "whittled on". It sounds like you are working to a target on double action weight. Better to install full length. Double action weight at 129 oz is right at 8 pounds. That is too light for a .22. My pre 19 double action is a nice smooth reliable 11 lbs 7.5 oz or in your terms 183.5 oz.

.22 ammo is not 100 percent reliable anyway and there is always some that do not fire on the first try. Maybe high dollar target ammo, like Ely, perhaps is closer to 100 %. Smooth and reliable is more important than trigger weight.

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Richard Gillespie
FBINA 102

Have you examined the indent on different fired cases for comparison. Agree with above - if S&W wanted the strain screw “whittled on”, they would do it themselves or just install a proper length (as I would believe they did).

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S&W factory revolver armorer

I’m aligned with the full sized strain screw, although I started with trying to match the 357 hammer weight spec. I was not trying to get a lighter pull, I was seeking reliability, and assumed the 357 weight was a good target, since I could not find a spec for the Rimfire.

I will measure what it is now, with the shim, for comparison.

I’m also going to try to blast out the firing pin as suggested above.

Does anyone have a spec for Rimfire firing pin protrusion? I’m wondering if it may be a hair short

If anyone has a definitive number for Rimfire hammer weight, that would be useful too.

Still learning!

I had acsimilar problem with a 1955 vintage K22. I replaced springs and then figured out someone had filed the strain screw. Replacing the strain screw fixed the problem. The one that was in it was quite a bit shorter.

Just to clarify current state. New mainspring. New (unmodified) strain screw. (Measured 55oz hammer weight.). Added shim from 22 case scrap. (Have not measured hammer weight yet.)

Attached Images

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A new rim fire main spring and screw are not the same as a new center fire main spring and screw. My suggestion of getting a new screw from Ace is so you have an over length screw to start with.

Just because one K22 works with a 55oz hammer weight does not mean yours will. To many other variables. They do not all have exactly the same headspace, endshake, firing pin length, firing pin spring etc. Don't get stuck on the numbers. Find what works

IF you start from 100% reliable and adjust to failure to fires you KNOW where your at. I have 4 K22s and everyone of them fires every time.

BTW Your firing pin should stick out about the thickness of a dime. Open cylinder, Hold thumb piece back, pull trigger and hold it back, slide dime beside firing pin tip

You will more likely need around 70 oz. + or - hammer weight to reliably fire rimfire ammo.

Edit to add - The mainspring on all K, L, and N frames is the same one. The original tapered S&W mainsprings are super high quality, and the ones I like the best. Also, because they are correctly tempered, you can bend or straighten them and they stay will hold that shape. The exception is the stainless steel ones that have an S stamped on them. Those do not work well.

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protocalldesign.com

Is there a difference in the Rimfire mainspring? I’ll certainly Google up Ace and see what they have.

70 Oz, wow! Ok, I’ll have that as a target.

All Ace stores have gun screw and I don't find them searching their web sites. The gun screws are found as one of the sets of the small boxes of various screws, fastener etc.

I have also found the same gun screw kits in the Big R farm and Ranch stores in this area of the country.

But you can use any 8-32 screw, but hardened ones are best. Some guys use ones with Allen socket heads, but the gun screw selection has ones with the same head as the factory. Plus, stuff like various scope mount screws etc from about 0-80 up to 8-32.

The kits also have a small metal plate with lots of marked screw sizes drilled and tapped in them. Not only are they handy for figuring out what size screw you have, they also work well to thread a screw in tight and hold it so you can grind or file it to the length you want