Super GP100 tuning

[Toolguy]

For making holes in hammers, you want a 2 flute, straight flute, solid carbide drill bit. They can be had at www.mcmaster.com. Use them dry with no cutting oil. An end mill doesn't work well for drilling holes. These walk right through. Run at 500 - 1000 rpm. You can use these on a drill press too, but mill or drill press, make sure the part is held securely or you might break the drill bit if it gets loose.

Edited June 27, 2022 by Toolguy

[mikeAZ]

 Toolguy, Thanks for the info!....

[Fishbreath]

3 hours ago, mikeAZ said:

Pics added... BIG difference in carbide mill quality... 

 

Those look great!

[Fishbreath]

Having now handled a really well tuned GP100, courtesy of Dave Olhasso at the IRC, I've been spending some time this offseason working on mine again.

 

One easy gain is trigger return spring: I found some that shave a full pound off of the trigger pull. Trigger shims were required to make the light spring work. 0.002" total was the sweet spot—one gun has 0.001" MCARBO shims (one on each side, like you'd expect), and the other has a single 0.002" TriggerShims.com shim, on one side only. Both seem to work roughly equivalently well. (There are centering bosses on the sides of the GP100 trigger. Presumably the one-sided shim helps the trigger ride on the boss only, rather than tipping and dragging on the side.)

 

I've had mixed success with lightened firing pin springs. They definitely make a difference in ignition, but the 9mm gun really chews them up fast. 300 trigger pulls, and one of my super-light ones was already just about worn out. The .357 gun seems to be a lot gentler on them; it's made it through a few thousand, and the spring is deformed a bit, but seems to be keeping its strength. (The factory ones deform, too, over time.)

 

Based on the above, I wonder if the received wisdom for Rugers ("file the hammer step down for better ignition") is wrong, at least for the more recent guns with the LCR-style screw-in bushings/firing pins. The gains from a light firing pin spring seem as least as substantial as the gains from filing down the hammer step. I can kind of imagine how a reduced hammer step might lead to increased stress on the spring, and therefore reduced spring life, but I admit I'm guessing a little here.

[mikeAZ]

I returned the Mc Carbo kit. Went with the Wolff kit. Ground about a coil off the trigger return spring (cut more?). With the included Wolff hammer spring, I'm getting flattened primers with Fed. 100's  and a wimp powder load. . Either of my trigger pull gauges give me a 8 # smooth trigger, of course I'd like less but I'd rather buy a GOOD reduced power kit than a homemade kit ..... I've milled  about 1/3rd of the hammer weight off (Bored holes). Seems the end of the Ruger Super GP100 x 9mm is near anyhow ??'. Jay, hope you get one with your Ruger certificate?. I got an email back from McCarbo... They have never had a Super GP100 x 9 mm to develop a trigger kit for it.

Edited January 15, 2023 by mikeAZ
added info to post

[Fishbreath]

I tried a fresh hammer on the 9mm Super GP, with no filing done to the hammer step, and it still chews up FP springs a whole lot faster than the .357. The only obvious visual difference between the two guns is the depth of the firing pin bushing. I have shims to set that, out of Bowen extended firing pin kits, so I'll test it soon. (I need to get more springs first, though.)

 

Still, the trigger return spring and the middle-weight firing pin spring option I'm testing (which lasts well enough in the 9mm gun) have me working with much better triggers for 2023—5lb measured at the very bottom of the trigger, which is the only place I can get a consistent reading, so probably 6-7lb where I'm actually pulling them.

[mikeAZ]

Best I can get is 7 1/2#'s with Wolff (-) hammer spring and cut trigger spring. .... My hammer is lightened about 1/3 of original.. Even using carbide end mills.... that hammer is tuff stuff.... I haven't shot the revolver enough to run into any major problems yet. I did ream the cylinder a bit as I check every 9mm  barrel/cylinder  for id with a Clymer finish reamer. Keep us informed on your progress... Thanks, Mikel

[Fishbreath]

I finally worked out why the .357 took more reset spring than the 9mm. It has to do with the trigger plunger (the small part with the triangular head in the trigger assembly, which engages the cylinder latch to unlock the gun during the trigger pull).

 

Some observation indicated that the initial timing window on the 9mm is small: the click of the cylinder latch locking again (i.e., when it's released by the trigger plunger and pushed against the cylinder by the spring) happens almost immediately after the latch has cleared the notch. On the .357, it's larger: the notch is 10-15 degrees gone by the time the latch locks.

 

The length of the nose of the trigger plunger controls how long the cylinder latch stays unlocked, and also how much spring force is required to snap it back over the ledge on the cylinder latch during reset. The factory springs, and even the Wolff lightened springs, are pretty strong, so there's a wide range of dimensions that will work. Lighter springs require more careful fitting. Shorten the nose of the trigger plunger, and you get easier reset with the same spring. It's easy to check in the gun—as long as the latch clears the notch before it locks, you're fine.

 

The Wolff 8lb spring pulls about 2lb on my trigger scale, with everything else isolated, and the springs I'm using now pull about 1lb. The reset is still pretty peppy, so it's more or less a free 1lb off the overall pull weight.

[Fishbreath]

(I hope you guys don't mind me using this topic as a diary!)

Today, I discovered that trigger shims bear on timing: my .357 has one chamber just out of time with a 2-mil shim on the left side of the trigger (pushing the trigger and pawl to the right of the frame, away from the ratchet), and all chambers in time with a 2-mil shim on the right side of the trigger (pushing the the trigger and pawl left, toward the ratchet).

[mikeAZ]

MY 9MM, Good info, I put 2 ea. .006's in mine and took the Factory .005's out. KEEP the info flowing!. Mike

[Fishbreath]

My .357 was right on the edge of out of time—put moderate or heavy drag on the cylinder, and the hammer would fall on one chamber before it locked. I didn't want to send it on another trip back to Ruger, which would have necessitated taking a bunch of my own parts out so they didn't get replaced with factory-spec stuff. Numrich, it turns out, sells factory-new pawls and trigger plungers, so over the course of a few evenings, a substantial number of ruined parts, and a lot of head-scratching, I figured out how to fit them and adjust timing.

 

Below are my notes, lightly edited. I don't stand by them 100%—not until I've done it a few more times—but it ought to be a good starting point if you're feeling adventurous. The most aggressive tool I used was a 240-grit diamond file. The most aggressive I was with material removal between tests was about as long as it took to scrape a sharpie mark off of a surface with the 240-grit file—5-8 strokes at most.

 

[notes below]

 

It's relatively easy to do this to factory standards, using a factory-weight or Wolff 8lb trigger return spring, but relatively tricky to do it to the standards ultra-light trigger springs seem to require.

 

During trigger reset, the return spring is pushing the trigger forward, which compresses the trigger plunger spring so that the trigger plunger spring can snap over the ledge on the cylinder latch. Those springs work against each other, so this is the limiting factor in how light you can make the trigger return spring, and it also requires fairly precise fitting of all of the parts.

 

Pawl

1. Start with the pawl. Take some off the back behind the nose (the factory doesn't, but it'll reduce the friction of the pawl against the frame), and then enough off of the tilt stop (the flat surface above and behind the axle/pivot pin) so that it slides into the frame without pulling the trigger and clears the cylinder release when the trigger is pulled.

2. Get the pawl nose shaped right by taking material off of the left side of the nose. Go very slowly and check frequently. At first, the trigger won't go all the way back, then it will go all the way back and hitch/bind between the frame and ratchet, then it will go all the way back smoothly. Get just over the line. I haven't needed to take material off of the top yet, and I think it's probably easier to fix early cylinder movement with a new trigger plunger.

 

3. You may need to take more off of the tilt stop if the cylinder starts moving late, but I don't know

ONLY POLISH THE OUTSIDE FACE OF THE PAWL. It presses against the frame to give the pawl a fixed reference point. The width of the entire top of the pawl, the shiny part above the arm, is a timing-critical dimension.

 

Removing material from the tilt stop will advance latch pop-up by reducing the force holding the plunger in a forward position, and slightly reduce required reset force, and start the cylinder turning faster. It seems to change timing faster than it reduces reset force.

 

IGNORE RESET UNTIL THE PAWL IS CORRECT.

 

Trigger Plunger

1. Fit.

Removing material from the underside of the nose will retard latch pull-down. It also will advance latch pop-up slightly.

Removing material from the front/top of the nose will advance latch pop-up and somewhat reduce required reset force. A more vertical front face is better for reset: the steep angle means the cylinder latch will contact it at one point, rather than all along the front face's length.

 

Removing material from the cut at the back of the plunger will reduce required reset force and slightly advance latch pop-up. A little goes a looong way.

 

There isn't any way to retard latch pop-up except fitting a new plunger. Err on the side of too little adjustment before checking.

 

Theory: get it close, i.e. to within about one cylinder latch width of the notch, then take material off the back to reduce reset force to below the required threshold without a hammer spring. You may need to take a little tiny more off to make it work with a hammer spring, but see next paragraph.

 

If it's dead nuts reliable without a hammer/spring but has issues with, try oiling the sides of the trigger. If it runs perfectly for a little while, or if it only exhibits the problem if you push the trigger to one side while letting it reset, add more trigger shim.

 

Symmetry may matter. One of my guns doesn't care whether it's shimmed with one 2-mil shim on one side of the trigger, or two 1-mil shims, on one each side of the trigger. The other isn't happy with one 4-mil shim, but works great with a pair of 2-mil shims.

 

Final Fitting

If there's some grit toward the end of the trigger pull, look at the gun from the right side while pulling the trigger, and observe the very front edge of the pawl. If it touches the ratchet (i.e., if the tip of the pawl bottoms against the ratchet), take a tiny amount off at a time until it doesn't contact anymore.

[Fishbreath]

My big springtime project this year was recording everything I've learned about tuning up GP100s.

 

Having tried Olhasso's trigger at the IRC, I think he does better than me, but not by very much. Hopefully this is useful if you have a GP100 you're interested in slicking up.

[IHAVEGAS]

On 3/14/2023 at 10:30 PM, Fishbreath said:

My big springtime project this year was recording everything I've learned about tuning up GP100s.

 

Having tried Olhasso's trigger at the IRC, I think he does better than me, but not by very much. Hopefully this is useful if you have a GP100 you're interested in slicking up.

 

In a word.

WOW!!!

 

My life should slow down in a month or so and I want to take this on as a project.

Would you mind a quick reminder of what the final result was in pull weight with federal primers, I am sure it is there or here somewhere, just being lazy. 

[Fishbreath]

Very roughly 6lb-7lb with a trigger scale at the middle of the trigger, or 5-5.5lb at the bottom. (It's much easier for me to get consistent readings at the bottom of the trigger, since it's not sliding around on the curve.)

 

Of the useful tricks I've found, one of the handier ones is using M5 washers as spacers on the mainspring strut between the spring and seat, to preload the hammer spring a bit—it lets you adjust hammer fall weight almost as finely as a strain screw, which saves you having to jump all the way up to the next weight of spring.

[mikeAZ]

49 minutes ago, Fishbreath said:

50 minutes ago, Fishbreath said:

Of the useful tricks I've found, one of the handier ones is using M5 washers as spacers on the mainspring strut between the spring and seat, to preload the hammer spring a bit—it lets you adjust hammer fall weight almost as finely as a strain screw, which saves you having to jump all the way up to the next weight of spring.

I've only been to obtain the Wolff 8# hammer spring.... what are you doing  to this spring OR have you found a substitute? Mike,  

 

[Fishbreath]

@mikeAZ I assume you meant the trigger spring, since Wolff hammer springs only go down to 9lb. I have a source for lighter trigger springs, just trying to dial in what the lightest weight is that will work in most guns.

[mikeAZ]

my bad, keep us informed on the springs. mike

[Fishbreath]

My newer 9mm Super GP is, so far, resistant to ultralight springs, but I did find one that will reset my .357" 100% of the time, rather than 99.9%. I think the new 9mm gun needs a bit more trigger plunger work, and might also need a bit of pawl fitting to advance cylinder timing a bit, so I can run a shorter trigger plunger.

 

My 10mm Match Champion, so far the only 6rd Ruger I own, has a bit of staging to it in double action. A few chambers seem worse than others, which points to pawl/ratchet fit, but I don't have a good sense for that interaction yet, and don't want to mess with it until I'm done with the IDPA match this weekend.

[mikeAZ]

2 minutes ago, Fishbreath said:

My newer 9mm Super GP is, so far, resistant to ultralight springs, but I did find one that will reset my .357" 100% of the time, rather than 99.9%. I think the new 9mm gun needs a bit more trigger plunger work, and might also need a bit of pawl fitting to advance cylinder timing a bit, so I can run a shorter trigger plunger.

 

My 10mm Match Champion, so far the only 6rd Ruger I own, has a bit of staging to it in double action. A few chambers seem worse than others, which points to pawl/ratchet fit, but I don't have a good sense for that interaction yet, and don't want to mess with it until I'm done with the IDPA match this weekend.

 

[mikeAZ]

Following, with interest. Mike