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  #1  
Old 07-15-2018, 02:03 PM
flangster is online now

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GP 100 Trigger Job - 3.5 lb SA trigger pull+smooooth



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I wish I had thought to take pictures as I went along. But, seriously, I was following the Youtube video located here:

https://www.youtube.com/watch?v=O0jFwUq_-VU

So my pictures would just be superfluous. Also, after a while, my hands were pretty oily, and oil + photographic equipment? Not a great mix.

Taking the GP100 apart is disturbingly easy. But then again, it is easier to take a jigsaw puzzle apart than to put it back together.

Some of the Youtube videos out there show folks polishing away on various internal parts with grinding compound or Flitz and a Dremmel. Some of you have heard me say that around my house, power tools are also called, "yet another way for Dad to ruin perfectly good raw materials quickly." So I sprung for a small Translucent Arkansas whetstone from Dan's Whetstone Company. Surprisingly affordable and doubles as a knife hone. I also had some 2000 grit automotive sandpaper and some oil. I just used a cutting oil I had around. I am sure there is a specific one that is recommended by experts. I also had a utility knife blade to use as a backer for some of the smaller surfaces, a set of punches, and a screwdriver set. I planned to put in a set of lighter Wolff 10 lb trigger and hammer springs. I was going to have the revolver broken down, so: why not? The hammer spring is quite easy to change. The trigger return spring is alllll the way inside the trigger group. It was the last thing I removed and the first thing I replaced. Its retaining pin was the only pin I removed that required a hammer on the drift punch. All others requiring removal could just be pushed out with a punch under hand pressure.

The idea was just to polish the internal surfaces, not to remove any material or change any internal angles. There are a number of parts that have some friction in the GP100. The sear and sear engagement faces got a verrrry light touch with the 2000 grit sandpaper and oil. I went slowly, without pressing down too hard. A mirror shine takes a surprisingly small amount of time on any of these parts. The hammer engagement surfaces got some attention, as did any flat surface with interference/bright marks. The video copied above lays out the steps pretty clearly.

Some editorial additions to the video. There are two spring/detents in the trigger group -- each is a small cylindrical plunger with a small captive spring. I managed to get them out without having them sail into a dark corner (good news), but they are not interchangeable (bad news). Same diameter, different lengths. Ask me how I know. The more methodical among you will label them or put them in separate pill bottles or something in the order you removed them. The good news is for the idiots among us, the re-assembly of the trigger group only works if you get the correct spring detents in the right holes. In fact, this goes for all the parts. In the video above, there is just one goof where the guy making the video puts the part being re-installed accidentally out of the frame. But "hit rewind" enough times and you can see what he has done and what the proper orientation of the parts is.

I had a bit of a head scratcher putting the trigger group back in the frame. Something was bound and I never did figure out what. I suspect that I inserted the part that intersects with the cylinder's external notches backwards. More video rewinding. Took the trigger group partially apart again. Rewinded. Reassembled. And Presto! The thing snapped back into place. A little complicated, but a fascinating design. Also, while it is easy to see how the hammer strut is oriented, beneath the spring that surrounds the strut there is a retaining plate. I managed to insert that backwards while compressing the new Wolff spring under tension. If you do this on your pistol, you will find that the hammer spring now prevents the grip retaining screw from traveling through the frame to do its job. Simple to fix, but it took me a moment to realize my error.

End result? A very pleasant GP100 trigger. DA is still on the heavy side, but is smooth, smooth, smooth. Feels like the DA on my S&W Model 63. SA measures at 3.5 lbs. and breaks crisply. Overall, I would say it has been a success (at least to the extent that all the parts seem to be working together like clockwork). Whether or not the revolver will still have dependable ignition will have yet to be seen. I will say that the internals had few toolmarks or actual rough spots. All I did was take some parts that actually rub together (or otherwise have contact) and improve the finishing on them. The two or three places where I did see machining marks, I polished them with the 2000 grit sandpaper, but this was more because I do not hope to have the revolver broken down to this extent any time in the near future. Still, if that 10 lb trigger return spring needs to be swapped back ... I'll have to take most of the revolver down again.

All in all (and as a point of comparison), it was much more challenging to do a VQ sear and trigger replacement in a Ruger Mk II pistol than it was to get the GP100 taken down and put back together. That's because the Mark series of pistols have a couple of stamped parts that have to be held under spring tension while you are trying to reinsert pins in a cramped space. Not so, the GP 100. It really is like a jigsaw puzzle where the final product only goes together one way. The only potentially troublesome springs are the ones in the detents, and the spring forces are quite small. They are therefore easy to depress while moving the pieces that keep them captive back in to place.

As always, your mileage may vary and anyone doing his own internal polishing, particularly on sear engagement surfaces, does so at his or her own risk. But as 2-hour weekend projects go, this was pretty manageable.
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Old 07-15-2018, 10:15 PM
LorenatBMS

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I am looking forward to see how the 10lb hammer spring works in your GP100.

I was able to get mine down to the 12lb hammer spring with no failure fires.

Nice looking grips too!
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Old 01-30-2019, 04:44 PM
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I picked up my GP100 last Friday ( 5 days ago ). I ordered a set of Wolff springs the same day I ordered the gun. It warmed up to 34* two days ago, and I got a chance to put 80 rounds through it. After I figured out how to tame that big green blob on the front sight the accuracy was good, with no blow back, and it functioned as it should. When I get a chance I'll start another thread on that range session, and the accuracy.

Thanks to your thread, and a few videos, I done my first GP100 trigger job this morning. Beside the vid that flangster recommended https://www.youtube.com/watch?v=O0jFwUq_-VU I also recommend this one https://www.youtube.com/watch?v=WqG5_2egsck I was going to order a stone from Dan's Whetstones, but once I got to his site I found a few other stones that I thought I would get. Once they were added up it was going to cost more than the new set of Altmonts that I wanted so I backed out, and went another route. I got some 1500 wet/dry paper, and made some sand paper sticks. I had some of those wide popsicle type sticks that crafters use. I used spray adhesive on the paper, and stick, then trimmed with a razor blade. The only place I used the stick was lightly on the front face of the sear, and the inside of the frame behind the transfer bar, where the sides coincide with the hammer. I used a felt wheel on a Dremel with a red compound stick ( jewelers rouge ) to polish everything else. I polished every part covered in the two videos, and they shined like they where chromed.

The only part that isn't covered in the videos is changing the springs. I changed the trigger return spring after the trigger itself was out of the housing. I figured would it be under less pressure. When I removed the spring all the parts came out. The spring sets between two ends. The one that goes inside the housing has a recessed dimple on one end , and a rounded dome on the other. The recessed dimple goes against the trigger, and the domed end fits inside the spring. The one mistake that I made was putting that in backwards, and it will not let the trigger go back in the housing, no matter how many times you try. The hammer spring is under a lot of pressure, and can be a little bit of a challenge. I laid a pipe clamp on the table, and clamped the top of the strut in it. Then used a slightly open linesman plier to push down while removing the pin. Be careful , one slip and that part would be gone.

So trigger job done. Pretty easy, and took about 2 hours. Before doing it the SA pull was 4 # 6oz, with some take up, but not gritty.
I used the 12# hammer spring, and 8# trigger return spring. Now the SA is 2# 4oz, with a ever so slight take up. The DA is now around 6#, and smooooth. I couldn't measure it before, it was to heavy. I haven't got to test it for lite strikes yet. It's only supposed to get up to 9* tomorrow.

Anyway, thank you flangster for the write up, and making it sound easy. I figured it would be better to post this in your thread, instead of starting another, so anyone thinking of trigger work on a GP may get some enabling.
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  #4  
Old 01-30-2019, 06:47 PM
flangster is online now

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Very cool! In my revolver the 10# spring led to some light strikes. So I am back to factory. Single action is still crisp. The GP100 also had to go back to Ruger for some TLC on the forcing cone. But she is shooting well now:



Hope yours does well for you!
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