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.