HomeSmith Tech: Let's talk about springs

[Shotguncoach]

When I first started doing Smith & Wesson action jobs I was all over the place on spring weights. For the hammer spring, I would take each gun to the range and progressively back out the strain screw until I got misfires, turn the screw back in 1/4 turn past where the misfires stopped, and then shorten the strain screw so that it could be bottomed out and produce the same hammer tension.

It didn't take too long to figure out that all of them were right around 48 ounces. I stopped doing the misfire test on every gun and just set the hammer tension to 48 ounces on the bench. That technique has worked well for the last year.

Rebound springs though have been a different animal. For a long time I was on a quest to achieve the lightest possible trigger pull weights and still have the gun be reliable. I've gotten to the point now that "lightest possible" is no longer a good thing and I've had to back off......a 6 pound double action pull is cool, but the 18 ounce single action pull that comes with it is not something that most people can deal with.

It's time to put some numbers on rebound springs and find "my" combination to use going forward. In this article we're going to start with a stock, dirty gun and get some baseline measurements, then clean and lubricate it and take another set of measurements, then start messing around with spring weights to see what actually happens. We're going to go deep into rebound springs, then come back to the hammer spring and experiment with different ways to achieve the 48 ounce hammer tension target.

Some definitions:

- Hammer tension: the amount of tension in ounces required to move the hammer with the trigger in the full rear position.
- Trigger tension: the amount of tension in ounces required to hold the trigger in the full rearward position after the hammer has dropped.
- Double action pull: the average of 6 double action trigger pulls, measured in pounds.
- Singe action pull: the average of 6 single action trigger pulls, also measured in pounds.

Our test mule for this project is a 4" Model 19 from 1975 that probably has not been cleaned this century.



Our baseline numbers without doing anything other than checking to ensure the gun was empty:

Hammer tension: over 72 ounces (maxed out the 72 ounce scale)
Trigger tension: 48 ounces
DA pull: 10 3/8 pounds with a 1 3/4 pound variance between high and low
SA pull: 3 1/2 pounds, very little if any variance

 

[Shotguncoach]

Now that we have our baseline numbers, let's clean the poor thing and get some lubrication into the correct places.



I found several areas that needed attention while I was cleaning, but the only one that I fixed was the bent cylinder stop spring.

Measurements after cleaning and lubrication:

Hammer tension: 66 ounces
Trigger tension: 48 ounces
DA pull: 9 1/2 pounds with a 1 1/4 pound variance between high and low
SA pull: 3 3/8 pounds, very little if any variance

That's not quite a full pound off of the double action pull just from cleaning and lubricating. Our first lesson: clean your darn guns.

The next step was to do an action job and remove as much internal friction as possible with my tools and knowledge set. I'm not going to detail it all, but I did take 71 pictures along the way. If you want me to go to into detail of what I do, let me know and I'll post a thread about just that.

After the action job and still with the exact same springs used previously, here are the numbers:

Hammer tension: 62 ounces
Trigger tension: 46 ounces
DA pull: 9 1/8 pounds with a 1/4 pound variance between high and low
SA pull: 3 3/8 pounds, very little if any variance

Not a tremendous improvement in the pull weights, but a vast improvement in consistency. The dirty gun had 1 3/4 pounds from high to low in the double action pull, the clean gun had 1 1/4 pounds from high to low, and the action job brought that down to only a 1/4 pound from high to low. The single action pull improved by a few ounces from the cleaning, but then stabilized and did not change.

 

[Shotguncoach]

Now let's set our hammer tension....

For this part of the test, I cheated and just backed out the strain screw to change the tension. I got lucky and exactly 1/2 turn from bottomed out gave me 48 ounces, so that was easily repeatable.

Measurements with the strain screw 1/4 turn backed out:

Hammer tension: 56 ounces
Trigger tension: 46 ounces
DA pull: 8 5/8 pounds with a 3/8 pound variance between high and low
SA pull: 3 1/2 pounds, very little if any variance

So that took 1/2 pound off of the double action pull, increased the variance slightly (may have been my technique), and gained us 1/8 of a pound on the single action pull.

Measurements with the strain screw 1/2 turn backed out:

Hammer tension: 48 ounces
Trigger tension: 46 ounces
DA pull: 8 1/4 pounds with a 1/4 pound variance between high and low
SA pull: 3 1/2 pounds, very little if any variance

I apparently did a better job with the trigger pull gauge that time because out 1/4 pound variance came back. That's not a bad setup for a "service" gun, but we can do better.

 

[Shotguncoach]

The first set of rebound spring modifications are the ones we're all familiar with: cutting coils. Note: the hammer tension was reset to 48 ounces before all of the following tests.

One coil was removed from the factory 17-coil rebound spring and all the tests were repeated.



Hammer tension: 48 ounces
Trigger tension: 40 ounces
DA pull: 8 1/8 pounds with a 1/4 pound variance between high and low
SA pull: 3 pounds, very little if any variance

Not a tremendous amount of change here. The single action pull dropped by 1/2 pound, but the double action pull only changed a little bit. This would not be a bad carry setup at all. The trigger return is still quite snappy.

Now let's go to the the second most common phrase used here in the smithing forum: "cut 2 coils off the rebound spring". (The most common phrase is "check for dirt under the ejector star" )




Hammer tension: 48 ounces
Trigger tension: 36 ounces
DA pull: 7 5/8 pounds with a 3/8 pound variance between high and low
SA pull: 2 3/4 pounds, very little if any variance

Now we're getting somewhere. This setup still has a decent push on the trigger return yet feels well balanced.

Since our double action variance seems to have settled in and appears to be based more on my technique than the springs, I'm going to stop typing that part and only call it out if there is something major that happens.

Let's find out what these do..........


Working from strongest to lightest, here are the results:

Wolff 15 pound rebound spring
Hammer tension: 48 ounces
Trigger tension: 40 ounces
DA pull: 7 7/8 pounds
SA pull: 2 3/4 pounds

Wolff 14 pound rebound spring
Hammer tension: 48 ounces
Trigger tension: 36 ounces
DA pull: 7 5/8 pounds
SA pull: 2 1/2 pounds

Wolff 13 pound rebound spring (*most consistent trigger pulls)
Hammer tension: 48 ounces
Trigger tension: 34 ounces
DA pull: 7 1/4 pounds (same pull every time)
SA pull: 2 1/2 pounds

Wolff 12 pound rebound spring
Hammer tension: 48 ounces
Trigger tension: 32 ounces
DA pull: 7 1/4 pounds
SA pull: 2 1/4 pounds

Wolff 11 pound rebound spring
Hammer tension: 48 ounces
Trigger tension: 26 ounces
DA pull: 6 3/4 pounds
SA pull: 2 pounds

Yes, there is overlap in those numbers. Every spring is an individual. The 11 and 12 pound springs very much did not have the "snappy" trigger return that some people prefer. I've taught myself to get my finger out of the way, but I can outrun the trigger and start the next pull before it has fully reset if I'm not paying attention.

The most consistent and balanced setup for my taste was the 13 pound Wolff spring, but the 14 pound Wolff and the factory spring with 2 coils removed were very, very close. There's a reason why conventional wisdom is conventional: cutting two coils off the rebound spring works well. If for some reason you don't want to cut your original spring (or if you don't have it anymore), try the Wolff 13 and 14 pound springs and see which ones you like the best.

Tomorrow we'll do some experimenting with hammer springs and alternative ways to get to 48 ounces of hammer tension.

 

[-BTM-]

What is your setup for measuring hammer tension? For example, Do you get it started then hook it under the firing pin, or is it at the spur?

 

[richrd]

Very interested and please post what steps you take to smooth the action

 

[mtgianni]

Great write up of your process.

 

[bigggbbruce]

13lb rebound spring and reduced power main spring is my go to set up.
Any less spring tension, less reliable gun.

 

[SS336]

Very interesting post, thanks for putting in the time to do it.
Now a couple of questions.

Why do some revolvers return just fine with 13# rebound springs and some don’t?
Some of my revolvers are sluggish on the reset. Some loosen up with use.
I know I could just put in a heavier rebound spring, but….

 

[Fullmetaljacket]

I have a selection of Wolff reduced power rebound springs and plan to do a little experimenting. Thanks for the info in your post, good stuff. I've probably read this somewhere but I can't recall: what lb. rating is a factory 17 coil spring?

 

[Matt_X]

Very interesting post, thanks for putting in the time to do it.
Now a couple of questions.

Why do some revolvers return just fine with 13# rebound springs and some don’t?
Some of my revolvers are sluggish on the reset. Some loosen up with use.
I know I could just put in a heavier rebound spring, but….

I'm going to guess the reason may be the lengths.

When we measure things like trigger force and hammer force we are measuring the effect of both spring rate and the spring's length.

If that is hard to picture, think about this.
Cutting a spring does not reduce its rate, but does reduce the spring force at full extension.
Whatever force it had applied at nearly full extension before cutting, is now zero afte cutting two coils off.

 

[Shotguncoach]

There are a whole lot of things happening during the trigger return stroke and the spring has to overcome all that accumulated friction. An 11 lb spring in a stock action may not be able to completely overcome the friction and the trigger may “stick” halfway. Where I’ve seen that happen the most is the point where the trigger hook is trying to move the cylinder stop out of the way.

That thought just made the think of something else that may contribute: I’ve been smoothing the outside of the cylinder stop, but I haven’t been smoothing the interior of the slot where it rides on the stud. I’ll add that one to my list….

 

[-BTM-]

Just to

I'm going to guess the reason may be the lengths.

When we measure things like trigger force and hammer force we are measuring the effect of both spring rate and the spring's length.

If that is hard to picture, think about this.
Cutting a spring does not reduce its rate, but does reduce the spring force at full extension.
Whatever force it had applied at nearly full extension before cutting, is now zero afte cutting two coils off.

thats an interesting point, but I don’t think the rebound spring is ever at full extension unless you cut it wayyyy short

 

[Protocall_Design]

The main part of the cylinder stop that needs polishing is the angled face that the trigger interacts with when returning forward. The mating part of the trigger also needs polishing. On the older guns, that part is full width. On the newer guns, it's a little nub in the middle. Do NOT polish the nub off. The only time you need to do anything to the stop slots that ride on the pin is if the stop is not engaging the trigger enough to pull it down out of the cylinder at the beginning. Then you can use a rat tail needle file to make the slots longer to the front, thus allowing the stop to move rearward so the trigger can engage it more.

The rebound slide can be polished on the hammer seat and the front corner radiused. The bottom mating part of the rebound slide seat on the hammer can be polished and radiused. This will give less resistance to the rebound slide raising and rebounding the hammer. Always make sure that with the trigger all the way back and the hammer all the way forward, there is a gap between the hammer and trigger seats. If not, the hammer will hit the rebound slide as it comes down, and the RS will act as a shock absorber to the hammer strike of the firing pin. This is especially critical if you are adding a trigger stop.

As for the same rebound spring weight not working for all guns, there are many variables, like everything else. One is smoothness of the action parts, one is mainspring tension, one is personal preference for the feel of the trigger return. One is variations in individual springs.

 

[TheTinMan]

The OP is interesting and includes some good info.

I prefer a consistent and clean trigger break with a positive reset over light but squishy or inconsistent. What I’m driving at is the number doesn’t matter as much to me as how it feels and works for me. A lighter trigger pull isn’t necessarily better.

Recently I replaced the hammer on an Uberti SAA clone because the retractable hammer wasn’t working right and I wanted 4-clicks. Never having worked on an SAA before, I unknowingly bent the paper clip Uberti uses for a trigger/bolt spring and reduced the trigger pull to just under 2 pounds. That is just too light for me to feel safe, so I got a replacement leaf-style spring from Wolff and all is good now.

 

[Shotguncoach]

What is your setup for measuring hammer tension? For example, Do you get it started then hook it under the firing pin, or is it at the spur?

Good question - I should have included that.

I use an old RCBS "fish scale" trigger pull scale. I don't have enough hands to take a picture of the entire setup while I'm taking a measurement, but it goes something like this:

- verify the firearm is unloaded
- secure the barrel in a padded bench vise
- cock the hammer
- while controlling the hammer fall, pull the trigger and hold the trigger back
- insert the rod of the scale between the hammer and the frame in the notch just below the firing pin
- with the trigger still held back, pull on the scale to move the hammer to the middle of the stroke
- at this point there's kind of a dance that you do with the hammer and the scale, increasing and decreasing the pull on the scale while you watch the hammer move until you reach a balance point and you're simply holding the hammer in place. Look down at the scale and take your reading.

 

[Shotguncoach]

Very interested and please post what steps you take to smooth the action

Will do. It may take me a bit to put it all together around various doctor appointments this week. I'll start a new thread and hopefully get other people to chime in with their tips and tricks.

 

[Shotguncoach]

I got sort of a late start today, so this post may split into tomorrow.

After I finished making paper leaves and paper caterpillars for the childrens vacation Bible study project, I dove into hammer springs with a selection of popular springs on the market today. The goal was to find out if 48 ounces of hammer tension will produce the same trigger pulls no matter what spring produces that tension OR if 'how' the 48 ounce tension is achieved really matters. There's a chart at the end that sums it all up if you want the TL;DR version.



Here's how the springs look side by side:



...and here is how the stock spring sits in the gun when tuned to produce 48 ounces of hammer tension:



Since the 13 pound Wolff rebound spring produced the most consistent results in the earlier test, it was installed in our Model 19 test mule and stayed in place for all of the following tests.

The first hammer spring to be tried was the Wolff reduced power spring with the "power rib" .....and it immediately showed why there is a love/hate relationship with Wolff hammer springs. Using the strain screw that came with the gun, the Wolff hammer spring produced an initial hammer tension of only 32 ounces with the strain screw tight. It produced a 5 pound double action trigger pull, but that tension is way too light and would in no way be reliable.

Examining the strain screw, it was apparent that the screw had been slightly modified at some point. This is probably why I was able to get 48 ounces of hammer tension with the stock spring by only taking 1/2 turn off the strain screw.



This slightly modified screw had a reach of .470" measured from the tip to the bottom of the screw head. Scrounging around in the spare parts box produced a new replacement strain screw that had a reach of .482". This unmodified screw produced a hammer tension of 42 ounces with the Wolff spring, which is just enough to almost be reliable but will create light strikes occasionally. To make the Wolff spring work in this gun I would need to cut the bottom of the strain screw head to increase the reach and get the hammer tension up. I didn't really have the time to do that this afternoon so I just marked the Wolff spring as FAILED and proceeded with the rest of the test.

The Miculek spring produced the exact opposite results of the Wolff: it was way too strong. With the .470" strain screw all the way tight, the hammer tension was more than 72 ounces (maxed out the scale), the double action trigger pull was over 12 pounds (also maxed out the trigger pull gauge), and the trigger would not return after dropping the hammer. Loosening the strain screw 1 full turn did not change the results - still maxed out with a sticky trigger return. Two full turns off the strain screw finally dropped the hammer tension to 46 ounces. Going back to 1 1/2 turns out raised the tension to 54 ounces, and 48 ounces was achieved with the strain screw at 1 3/4 turns out.

Once the strain screw was tuned, the Miculek spring produced a very consistent 7lb DA pull with a 2 1/4lb SA pull.

The Miculek spring looks like this when it is installed and the tension is tuned to 48 ounces:



The Wilson spring was next, and with the .470" strain screw fully tight it produced a 62 ounce initial hammer tension measurement. At 62 ounces of tension, the DA pull was just slightly under 8 pounds and the single action pull was right on 2 pounds. Backing the screw out 1/2 turn brought the tension down to 52 ounces with a 6 3/4 pound DA pull and a 2 pound SA pull. Taking another 1/4 turn off the screw (3/4 turn total) produced the desired 48 ounces of hammer tension and a remarkable 6 1/4 pound DA pull with a consistent 2 pound SA pull.

Here is the installed Wilson spring, also tuned to 48 ounces. Notice the difference in the angle of the hammer stirrup when compared to the Miculek and stock springs pictured above.


I recall seeing a post from Protocall_Design about reshaping springs to achieve a more horizontal angle on the hammer stirrup, so I decided to to a bit more experimenting with the stock spring. The stock spring was taken to the garage where the big vise lives and introduced to Jim. Jim is a 3 pound ball peen hammer that belonged to my Grandfather....who was named Jim, oddly enough.



Why such a big hammer? It's all about mass. With Jim, I don't have to "swing" the hammer or "hit" the object. I just kind of let gravity bounce Jim off of whatever it is and things happen. I find I have much more control using slow taps from a big hammer than trying to speed up a small hammer to strike hard.

Anyway, after a few minutes of being massaged by Jim the stock spring had a nice curve in it. Interestingly, it took 1/2 turns out on the strain screw (same as the straight spring) to get to 48 ounces.

Here it is installed, at rest and with the hammer cocked:




Yes, it does clear the grip screw.

.......and here's what the reshaped screw produced for double and single action pulls:




So what did we learn? Here are how the various springs stacked up when all tuned to the same hammer tension of 48 ounces:

Stock - DA 7 1/4 lbs, SA 2 1/2 lbs
Wolff - Did not finish, crashed and burned
Miculek - DA 7 lbs, SA 2 1/4 lbs
Wilson - DA 6 1/4 lbs, SA 2 lbs
Custom - DA 6 3/8 lbs, SA 2 1/8 lbs

The Wilson is the clear winner from the 'off the shelf' group, but the custom bent stock spring is a very close second. It's important to note that ALL of the springs required tuning the strain screw to produce the best results. The way I did it for this test (backing the screw out) was simply for expediency and is not acceptable for a gun that actually gets used. For permanent use, the strain screw would need to be shortened (or lengthened if using a Wolff spring) and kept fully tightened. I'm going to stay with the custom bent stock spring to find out how it behaves over a longer period of time, so one of tomorrow's projects will be to shave the screw to work properly with that spring.

If you have other things that you've tried or additional data to share, please feel free to jump in and add your experiences to the thread. (Looking at you, Mr. Design. Or may I call you Proto? )

As a reward for being a good sport and having it's insides stirred repeatedly, our test mule was given a new set of shoes and introduced to the rest of the family.

 

[47knuckle]

Thanks for taking the time to write this up. What are the chances of getting you to work your magic on J frame with the external hammer?

 

[Lt.Donn]

What is your setup for measuring hammer tension? For example, Do you get it started then hook it under the firing pin, or is it at the spur?

The responses are very technical in these times. Back in the day, a smith would work on the action by feel, a little cut here, stoning there, polishing here and there, and checked their work in a couple of unique ways; a master factory smith I knew well, would cover the firing pin hole with his thumb, then pull thru dbl action...if the pin nearly broke the skin on his thumb, the tension was good...another time I watched as he held the revolver vertical, inserted a pencil, eraser first into the barrel, pulled thru dbl action and watched to see how high the pencil was launched by the pin...today all these "hacks" would be perceived as too subjective...but in the day, some marvelous PPC and duty revolvers were made this way.