Tuning the K and L frame

[Red Cent]

First, I have posted these questions on another site. Most all answers were polite and some were informative. I am interested in finding a consensus of a sort.

I am interested in the method(s) of tuning the K and L frame. The revolver will not be used for defensive purposes. Competition and practice.

It seems that beside the polishing and tweaking of the rebound spring (RS), the item that is left is the mainspring. One of the obvious answers is "Buy Wolf". I understand and accept that.

The other solution is the strain screw. Until recently, I was under the impression that was "the" way to a lighten trigger pull. Simply loosen the screw. Maybe loosen it til it misfires and crank it in a half or a quarter of a turn. Loctite.
As I have researched, a segment of gunsmiths advocate the same advise but, in addition, they measure the "left over" length and cut to size. I read a couple of articles referring to the "pyramid" shaping of the nose and using the ribbed leaf spring to give an audible click when turned. It would help to maintain the screw setting.
That is another thing I failed to ask elsewhere. What is the mushrooming of the strain screw?
The other bunch likes bending the spring. This is the most popular method. Apparently, the method is to put a small cylinder horizontally between the frame and spring and bring to full cock or just short of to start. The articles do note that excessive bending will change the geometry radically and may lock up.
Ran across some remarks of a guy named Carmoney. Apparently vey popular. He believes in bending and bobbing the hammer. Mathematics do back him on his thoughts on acceleration and kinetic energy.
I am a SASS shooter so I am not ignorant of bending springs. We do it all the time to the Winchester '97 mainspring. Some of us hourglass the mainspring along with the mainspring in our 1873 replica rifles. My match revolvers have 1 1/2# triggers. Same with the 1873s. Shotgun left kinda heavy.

First, I am going to experiment. Probably all the above. But I really want to know experiences of any or all of the above methods.
If you really want to tell me "Don't fix whats not broke", have at it. You're invited.

 

[RGPM1A]

I have always used an 8-32 hex key set screw to replace the strain screw with great success. Use a little blue Loctite on it to keep it from backing out. As long as you stay above a 9 lb DA trigger pull you should not have any issues with misfires with factory ammo. If you reload and use only Federal primers you can go as low as 7.5 lb with reliability as long as the primers are properly seated (in my experience - additional insurance against this can be obtained by using an aftermarket extended firing pin if you have a frame mounted rather than a hammer mounted firing pin ). For lighter SA pull you need to go with a lighter rebound spring. A 13 lb one will usually result in an SA pull of 2.25 to 3 lb. If you wish to get a lighter SA pull you will need to polish the trigger/cylinder stop engagement surfaces and rebound slide spring tunnel and rebound slide/frame where it slides in the frame to allow use of a lighter rebound spring w/o having trigger reset issues. I never have used a rebound spring lighter than 12 lb because in some revolvers it will result in an SA TP of less than 2lb - not wise to go lower than that because if the SA engagement surfaces have been fooled with or not cut correctly at the factory you WILL experience hammer push off issues. If you don't really, really know what you are doing never stone or polish the SA or DA trigger/hammer engagement surfaces because you can ruin the parts and/or render your gun unsafe.

You should note that simply replacing springs will yield lighter DA and SA trigger pulls but a truly fine light and smooth DA trigger pull requires a lot of other work. SA pulls in S&W resolvers are usually very light and crisp with a simple spring change. If you get creep or push off issues then you need to have someone who really knows what they are doing look at the SA hammer/trigger engagement surfaces because they are probably not cut correctly.

Another issue to consider when using light DA trigger pulls is the effect on ignition of the primers. Some have done work (Scooter) that shows that accuracy can suffer if the hammer is striking the primer with marginal force. I have found this to be true but can be mostly avoided with Federal primers and firing in SA mode only - like in bullseye shooting.

FWIW

 

[imashooter2]

Look at the contour on this spring from Wilson Combat:

Wilson Combat Custom-Tune Spring Kit S&W K, L, N-Frame - MidwayUSA

It is a simple matter to build a quick jig with 2 nails and a piece of scrap lumber to duplicate it. I've done a few. I put a piece of tape on the jig and mark how far I've moved the base when bending. This gives me reference for making adjustments.

FWIW, the spring that came in my Performance Center 627 was bent that way.

 

[Red Cent]

Whoa. That seems to be more abrupt and higher on the leaf than expected. That would be hard to duplicate by putting a small rod between the frame and the spring and cocking rhe weapon. Never tried it (yet).

Traded for a very nice M60-10. After some polishing, two coils off the rebound spring and two coils off the mainspring resulted in a little over 8#s DA. I reload and I do use Federals. my cowboy guns would not fire anything else.

I also just finished working over a Dan Wesson 15-2. I got the DA down to 8 1/2#s. Unique short stroke on the DA.

I use both in a competition called PCCA:

Home

The J frame is in Pocket Carry class and the Dan Wesson is in the Discreet Carry class. Both really run well.

Since the rules are quite broad, I want to build a heavy barrel 3" K frame. Maybe find a beater 686.

Did you cold form the spring with the jig?

 

[imashooter2]

I wouldn't try to bend a spring while in the gun. Seems like a recipe for disaster to me.

Yes. Cold formed. Place the hooks on one nail, use the second as a fulcrum, apply pressure to the base. Mark the tape with a pencil and release the pressure. See how far the spring has bent. Go slow, it is easy to add more bend, a little harder to take it back out. When you get the bend that looks right, install it and test the pull. Adjust as required.

 

[cyberiad]

As part of his competition work Carmoney does "bob" the hammer but the hammer is not "bent" in any way. He didn't devise the technique, it's been done to competition revolvers for a long, long time.

I think a nice action can be achieved with lighter replacement springs but cutting coils always seems like a bad idea to me though I know it's frequently a solution.

 

[tomcatt51]

Wolff hammer/main springs work well. The difference between the std and reduced power is how much arch the spring has. Some PC guns come with Wolff reduced power main springs. There's a S&W part # for it. The reason you bend the spring is to shorten it's installed (chord) length to maintain the correct geometry of the hammer stirrup or link. As you decrease spring preload by backing off the strain screw the spring gets effectively longer (less arch). Bob the hammer. On an MIM hammer we do a pretty radial cut and literally reduces it's weight by 50%. 5 1/2 to 6 lb DA pulls are pretty common.

 

[scooter123]

I've been conducting some controlled experiments with my models 67, 620, 610, and 617. Along the way I've learned a few things.

One is that the rebound spring has the greatest effect on the Single Action trigger weight. At one point I had the trigger on my 617 tuned to a 1.75 lbs. single action pull and IMO it's too light to be safe in a revolver. Personally I believe that 3 lbs. is perfect and wouldn't go any lighter. As for specifics, depending on the gun either a 13 or 14 lbs. rebound spring will produce a Single Action trigger weight of 3 lbs. I'll also warn you that going lighter that 13 lbs. on the rebound spring may cause trigger return issues, if you want to use a 11 or 12 lbs. rebound spring you'll have to spend a lot of time eliminating any "drag" on the rebound slide.

I've measured the sear creep on my S&W revolvers and it measures between 0.015 and 0.017 inch, combine that very short amount of creep with a very light trigger and it's an invitation to an AD. Had 2 AD's with the 617 and fortunately the only result was a huge flyer on the target, however on both occasions the gun fired when I "thought" all I was doing was placing my finger on the trigger.

Second, I've been using a Dremel to shape shim stock so that I can use a shim under the head of the strain screw. Outside diameter is 0.218 inch and inside diameter is 0.147 inch. By doing this I've been able to tighten the strain screw fully so it won't shoot loose and be able to reverse any adjustment that didn't work.

Third lesson, hammer weight matters and NOT in the direction that one would expect. Quite simply, the ignition of the primer is a result of the transfer of Kinetic Energy, NOT Momentum. Since Kinetic Energy is a function of Mass times the Square of the Velocity, this means that a lighter hammer requires LESS power from the mainspring than a heavier hammer. As a result, a Service hammer can be made reliable with a lighter DA trigger pull than a Target Hammer. Currently my 620 is 100% reliable with any ammo I've been able to find at 8 lbs. 0 ounces. On the other hand my model 610 is set to 9 lbs. 0 ounces and while I haven't done it yet I feel that the limit for reliable function will be at about 8 1/2 lbs., when I tried it at 8 lbs. even it misfired at a 30% rate. If you bob the hammer I believe that 7.5 lbs will prove reliable with any ammo.

Fourth lesson, shoot the gun for at least 1000 rounds with the factory setup. It will provide 2 benefits. One is you'll gain strength in the trigger finger. The second benefit is that it will produce rub marks in the frame recess or sideplate that will indicate areas that need a bit of smoothing with some wet sandpaper. For the ideal tuneup you'll want to have a final result that doesn't rub anywhere on either the trigger or the hammer.

As for going even lighter with the DA trigger pull you'll have to start getting a bit exotic. Basically, it will become essential to eliminate any "drag" between the hammer and the frame or sideplate. That means thinning the hammer to the only area in contact with the frame and sideplate is a small raised boss surrounding the pivot pin. There are also some 3mm ID needle bearings on the market that might also be used for the pivot pin but I haven't yet taken the time to measure the exact diameter of the factory installed pivot pin. However, for someone with the facility or capital, IMO it may be possible to get the DA trigger pull down to the range of 5 lbs. but it will take a good bit of work to get there.

PS; for reliability testing all of my centerfires have been tested for reliable ignition using Speer Lawman ammunition due to Speers reputation for "hard" primers. Subsequent tests using Winchester, Remington, and Federal ammunitions has shown that all 4 brands function with 100% reliability for ignition.

 

[Silverbullit]

Pictures of radial cut hammer?

Wolff hammer/main springs work well. The difference between the std and reduced power is how much arch the spring has. Some PC guns come with Wolff reduced power main springs. There's a S&W part # for it. The reason you bend the spring is to shorten it's installed (chord) length to maintain the correct geometry of the hammer stirrup or link. As you decrease spring preload by backing off the strain screw the spring gets effectively longer (less arch). Bob the hammer. On an MIM hammer we do a pretty radial cut and literally reduces it's weight by 50%. 5 1/2 to 6 lb DA pulls are pretty common.

Sounds very interesting, I would very much like to see your custom radial cut hammer tomcatt51, you don't happen to have a picture for us?

/Silverbullit

 

[tomcatt51]

Sounds very interesting, I would very much like to see your custom radial cut hammer tomcatt51, you don't happen to have a picture for us?

Sorry but no, my digital camera died. Draw a straight line from the stirrup attachment point to the top of the hammer. Leave about 2/3 of the hammer depth at the top. That should give you an idea how much to cut off.

 

[MMA10mm]

Look at the contour on this spring from Wilson Combat:

Wilson Combat Custom-Tune Spring Kit S&W K, L, N-Frame - MidwayUSA

It is a simple matter to build a quick jig with 2 nails and a piece of scrap lumber to duplicate it. I've done a few. I put a piece of tape on the jig and mark how far I've moved the base when bending. This gives me reference for making adjustments.

FWIW, the spring that came in my Performance Center 627 was bent that way.

Yep, this was "invented" (or better to say, made "famous" as I'm betting it was being done before by many) by 300 Gunsmith Service out of Colorado. Fred Sadowski. He bent the spring even farther up the leaf, probably 1/3 of the way closer to the hooks than the Wilson unit. But, this is a very smart/easy improvement that is pretty reliable and easily reversible.

One is that the rebound spring has the greatest effect on the Single Action trigger weight. As for specifics, depending on the gun either a 13 or 14 lbs. rebound spring will produce a Single Action trigger weight of 3 lbs. I'll also warn you that going lighter that 13 lbs. on the rebound spring may cause trigger return issues, if you want to use a 11 or 12 lbs. rebound spring you'll have to spend a lot of time eliminating any "drag" on the rebound slide.

I've measured the sear creep on my S&W revolvers and it measures between 0.015 and 0.017 inch, combine that very short amount of creep with a very light trigger and it's an invitation to an AD.

Second, I've been using a Dremel to shape shim stock so that I can use a shim under the head of the strain screw. Outside diameter is 0.218 inch and inside diameter is 0.147 inch. By doing this I've been able to tighten the strain screw fully so it won't shoot loose and be able to reverse any adjustment that didn't work. (This is unnecessary if you use the Wilson spring shown above, but I also like Scooter's technique, if you just want to "adjust" the factory spring that comes in your pistol.)

Third lesson, hammer weight matters and NOT in the direction that one would expect. Quite simply, the ignition of the primer is a result of the transfer of Kinetic Energy, NOT Momentum. Since Kinetic Energy is a function of Mass times the Square of the Velocity, this means that a lighter hammer requires LESS power from the mainspring than a heavier hammer. As a result, a Service hammer can be made reliable with a lighter DA trigger pull than a Target Hammer.

Fourth lesson, shoot the gun for at least 1000 rounds with the factory setup. It will provide 2 benefits. One is you'll gain strength in the trigger finger. The second benefit is that it will produce rub marks in the frame recess or sideplate that will indicate areas that need a bit of smoothing with some wet sandpaper. For the ideal tuneup you'll want to have a final result that doesn't rub anywhere on either the trigger or the hammer.

As for going even lighter with the DA trigger pull you'll have to start getting a bit exotic. Basically, it will become essential to eliminate any "drag" between the hammer and the frame or sideplate. That means thinning the hammer to the only area in contact with the frame and sideplate is a small raised boss surrounding the pivot pin. (This is one possibility. The man who taught me "things" described that most custom gunsmiths in the 50s-70s accomplished this by polishing the heck out of everything inside - two mirror-smooth surfaces with a thin coat of oil glide past each other really well, hence a lighter-feeling trigger pull. But, in this day and age of machinists and CNC equipment seemingly everywhere, Scooter's idea here has good merit, as it would be quick to do, if someone wanted to set up a machine to just mill away enough material to prevent the surfaces from touching at all.)

Extremely good info Scooter!


One last thing I'd add - For me, trigger pull is more than springs, weights, and smoothness - there's also what I call "interface". I round-over and polish the trigger face and use modified/semi-custom grips so that my hand geometry is as ideal as possible with the revolver's frame and trigger as well. It's not something that can be weighed/measured, but it's a factor on how well I shoot, and I think it would be for others too.