Hammer spring questions

[redlightrich]

Hello all, I am hoping that someone with experience can help me with these questions.
I have a Ruger GP100 in .22lr, that I have been "tuning". In an effort to lower trigger pull effort, I installed a Wolff spring kit. For purpose of this question, I will focus only on the hammer spring.

Mistake number one is I DO NOT know what the factory hammer spring is rated at in pounds.

In my Wolff kit, there were 3 hammer springs, the heaviest was 12#. This is the spring that I installed. Naturally, the trigger lightened, but I have some FTF with this arrangement. It is however very close to ideal. If I thoroughly clean the chambers, I can get about 2 ftf's in the first 100 rounds. After that, when the chamber is nice and gunked up, I get about 1 ftf per cylinder full on most ( not all) reloads. This is a 10 round wheel.
In studying the FTFs ( I have not yet determined if it is the same chamber that FTFs, but I have a suspicion) the non firing pin marks are very similar to ones that actually fired. Some of the FTFs are ammo related as I take the non firing rounds, and spin them to give a fresh area and still no bang. I am using various types of cheap bulk ammo. In my thoughts, the ability to use cheap ammo is one benefit of a revolver. I have used some good ammo as well, and although it gets a little better, it is clear to me I need a stronger whack!!

My guess is I need to raise the hammer spring pressure just slightly to eliminate the FTFs. I would think a 13# spring would all but eliminate any issue. It is that close

Can I shim the spring? I know when I was in my previous life as an automotive machinist, I used to routinely install spring shims. This was done in an effort to restore valve spring pressure ( on cheap rebuilds) or to fine tune pressure when installing all new parts. I had a spring pressure gauge/stand, which took any guess work out of the equation. I set the compressed length and read the gauge when closed on a spring. I added the shim, and took a measurement, and made sure there was no chance of binding. Yes I am over simplifying what occurred, but that is the basic idea.
Shims were either .030 or .060 for used springs, and of various sizes for fine tuning new springs. I personally never used any shim below .015 due to my fear that it may "rip" or tear when in service.

My automotive machine days were a long time ago. I no longer remember the actual numbers and percentages that the shims added to the pressure reading. I do know the springs were very thick wire and about 1.750 free length with pressure that exceeded 150 psi.

Does anyone have any input on this? How much pressure would be added if I installed a shim of say .020 or .030? I realize I can simply buy a heavier spring, but that defeats my "tuning".

I like the current trigger, and would like to up the pressure just enough to end the FTFs. This will never be a defense gun, so I am not afraid of the potential to very rarely FTF. It is a range gun, no competition, so very close, is good enough..

I have already ordered actual hammer shims ( this is to remove any potential drag that can occur if the hammer rides against the frame). These shims have nothing to do with the hammer spring pressure, although any reduced drag can help here.

Any engineers out there can weigh in? Has anyone ever used shims to raise the pressure? Of course I will be sure to check that the shim does not make the coils bind at full compression.

Thank you for reading my long winded request for help!!!

Rich

 

[Jim Watson]

Wolff says standard is 14 and they do not make a 13.

I see no reason not to shim the 12. It isn't going to hurt anything if you avoid binding, and you have the gun, the spring, and the experience.

Have you changed the trigger return spring? Wolf has 8 and 10 lb springs, 12 standard.

Of course anything you can do to reduce friction will help.

 

[Gunplummer]

I bought a brick of Remington .22's and about 2 out of 10 misfire. Sometimes turning them in the chamber helps and they fire, sometimes not. Could just be bad ammo.

 

[Slopemeno]

Years ago Clark used to make an adjustable mainspring strut for the Ruger Security Six series- so it's doing the same thing in effect.

DA revolvers in .22 LR always end up with heavier than centerfire DA pulls, so get it to the point where it's reliable.

 

[g.willikers]

How about just using good old trial and error?
Add a shim, go shoot it.
If it still isn't enough, add a slightly thicker shim and go shoot it.
A box full of magazines (the kind you read) will stop a .22.
You won't even have to go to the range to test it.

 

[straightshooterjake]

On a range only gun, I see no reason not to experiment with adding shims. If you have problems you can always put the gun back the way it was. Also, if you are willing to post a picture, I would be curious to see exactly how you install the shims.

If you are really trying to fine tune the trigger pull, then I would also suggest carefully examining the hammer for any signs of drag that might be draining hammer energy. On some guns stoning the hammer, or the frame, or installing shims on the sides of the hammer makes a difference.

Also, there is a modification to the hammer which can increase striking strength. You can take .020 off the top step of the hammer.

Post #7 in this thread describes modifying the top step of the hammer:

http://rugerforum.net/gunsmithing/9741-does-return-spring-sp101-lbs-matter.html

And post #5 in this thread has a picture with the "top step" of the hammer labeled:

http://rugerforum.net/gunsmithing/9908-gp100-hammer-modification.html

I hope it is OK to post links to another forum. These links are the best documentation I could find for this procedure.

Note that Ruger will not sell a hammer, so if the hammer is accidentally damaged then the gun has to be returned to Ruger. Also, those threads talk about advantages to lightening the hammer, but that is only for centerfires. Rimfires need a heavy hammer for ignition.

As you make progress with tuning, I would be interested to know the trigger pull weight on your tuned trigger.

 

[redlightrich]

Thank you for all the intelligent replies. This forum has so much wisdom in it.

When I disassemble and install shims, I will post the pix. I have read that the factory hammer spring is 14# but I believe that is for centerfire, such as .357 magnum. I would think that the rimfire would require more tension. My guess is that the rimfire spring is at least 17#

I will say, that the factory hammer spring felt considerably heavier than what I installed. I needed tools to put the factory spring on and off, where with the 12#, I simply stabilized the hammer strut in a notch in a piece of wood, and hand pressure was enough. I realize this is not scientific proof, but it sure felt like much more than 2# difference.

I find the hammer mod interesting. Yes, I did check, and Ruger will not sell a spare hammer, so I need to tread lightly there.

Yes, during my most recent test, I was running Remington bulk box, Golden Bullets, 36g hollow point. Now that I think of it, this box also created issues in my 1911 conversion, which usually eats the Rems like the gun was designed around that ammo. This may have been an unusually out of spec batch.

I studied the hammer, and I only see the slightest of frame rub on it. At any rate, I am shimming the hammer so it is centered in the frame slot, and will not lose force due to rubbing.

I installed the 8# trigger return spring, and tested it ( without the hammer installed) and it cycles the cylinder and other trigger related parts perfectly. There isn't even a hint of weak return, so I am good there.

My next move is to sand the hammer strut "tail" edges smooth, so there is no chance of friction . I already polished the top part that engages the hammer. I also broke the edges. Any reduced friction should help.

All in all, this is a nice gun. I don't shoot it as well as I would like. I thought I would be more accurate with it than I am, but I need to practice with it more after I slick it up better.

Thank's for the magazine idea. I would have to do that when my wife is out. She would not appreciate me firing the gun in the garage!!!!! Even if she understood, my dogs would go crazy, and that would make her even more mad!! The joys of marriage.

I will keep everyone posted on my findings as I work thru this, and will post pix of the hammer spring shims ( after I find something suitable).

Thank you all very much

Rich

 

[Clark]

I have found I can shoot primers off at home when the wife is home.

I push the muzzle into an old piece of carpet on the floor out in the shop.

Lots of ventilation. The wives can smell a gunshot.

I would practice while she is gone. Your cylinder gap may be big enough for supersonic gas escapement.

 

[straightshooterjake]

I want to follow up about the Remington rounds used in your testing. Just as centerfire primers can vary in hardness, rimfire rounds can vary in sensitivity to hammer strike. If I think some rounds are out of spec or defective, then I would not use them for testing. But if I know certain brands require a hard strike, then I intentionally use those brands for testing mainspring strength. I make sure the mainspring will ignite hard primers, and then I know that whatever ammo I bring to the range will work.

Some people set up competition guns with springs that will only ignite soft primers. This arrangement gives the best possible trigger pull, and it can still be 100% reliable with the right primers. But for most guns I prefer springs that will ignite any properly manufactured commercial ammunition. With polished internals and moderately lightened springs you can get a good trigger pull and reliability with all types of ammo.

 

[redlightrich]

Hello all, as promised here are the pix. I have decided to buy a Wolff 14 pound spring, which I believe is lighter than the factory spring. Wolff lists all models as 14# but I think that excludes rimfire. I doubt Ruger would set a CF and RF the same way.

I also install hammer shims to avoid any drag. I decided to buy the 14 after realizing there wasn't a lot of room to shim on the spring, so for 5 dollars, I am at 14#.

The pix of the springs show a 14, factory and a 12#. You can see how much thicker the wire on the factory spring.

I also swapped out the grip for an inexpensive Hogue. The factory grip just doesn't feel right.

Thanks again for the replies and ideas.


Rich

 

[redlightrich]

And one of the gun just for the heck of it