Ruger GP-100 mainspring

[Rugrev]

Anyone have any idea on where to get a lighter mainspring than the Wolff 9 lb one? Wonder what a Bullseye kit mainspring weight is if one can find one?

[Flexmoney]

Rugrev,

I'll move this over to the Revolver Forum for more eyeballs on the topic. (You posted it correctly in the Spring Forum, but it might get a better response in the Rev forum.)

Kyle F.

Forum Administrator

[Toolguy]

Brownell's is about the only place I know to get Ruger spring kits. If you can't find a lighter spring, you can always cut off a coil or 2.

[Bubber]

Steve Thorton has a way to lighten the Ruger mainsprings by grinding away the out side of the spring and keeping it full length. I just put the spring on a small enough rod to allow it sping when making contact on the sanding wheel and take away material to make the tension less. It is a trial and error method when I do it though. Good luck later rdd

[Rugrev]

I had forgotten about the grinding of the outside of the spring. Thanks, Bubber. I had a Ruger that a gunsmith had done this on. I might give this a try. I am seeking to get the DA on the GP below 7.25 lb or so where it is now.

Edited October 23, 2010 by Rugrev

[Flexmoney]

Let me know how it goes. (Take pictures?).

I've got a GP100 right here that needs some attention.

[wide45]

My GP-100 would not get consistent ignition with anything less than the factory spring. I was not using Federal primers, but I have doubt's that you can go all that low.

[GlennRasch]

Steve Thorton has a way to lighten the Ruger mainsprings by grinding away the out side of the spring and keeping it full length. I just put the spring on a small enough rod to allow it sping when making contact on the sanding wheel and take away material to make the tension less. It is a trial and error method when I do it though. Good luck later rdd

That is a AWESOME idea ,I must try that.......... thanks

[SteelShooten]

Anyone have any idea on where to get a lighter mainspring than the Wolff 9 lb one? Wonder what a Bullseye kit mainspring weight is if one can find one?

Was there a happy ending to this story?

I recently went to try a reduced force mainspring in a GP-100.

I bought a new mainspring and found it was shorter than the one already in the gun; different material apparently as well. Just dry firing, I considered the new spring to be about the equal of the old one so I lopped a coil off the new spring and tried it. It seemed a bit lighter.

Another half coil and it started to become more noticeable. Double action pull was still about 10-lb.

Another half coil. Now the action feels considerably sweeter than with the original spring. It feels light though the double action is about 9+ lbs.

Before I cut anything off the spring, when the hammer was dropped and the trigger held, the firing pin would continue to protrude from the breech. Not now.

When the hammer falls, it does its job but the firing pin spring can now 'help' the hammer to rebound off the frame so this may be the limit without tinkering with the firing pin spring.

What is nice is that when dryfiring, the front sight remains perfectly centered in the notch through several complete cycles.

I fired a few primed cases using orphaned pistol primers and they all fired without hesitation. Rifle primes ignored the tiny dent (the original mainspring can set off Wolf small rifle primers).

I'll have to plink with the gun for a while to see if I need to shim the mainspring now but so far the prognosis is favorable.

[ben b.]

As I undertsand it, shimming a cut spring should increase the force needed to compress it to more than the uncut spring initially required.

[SteelShooten]

As I undertsand it, shimming a cut spring should increase the force needed to compress it to more than the uncut spring initially required.

It depends on how much of a shim you use. I look at it more like cutting the spring is coarse tuning whereas shimming or grinding is fine tuning.

Instead of cutting the spring shorter, if you grind away the OD it may not be possible to shim the spring back to its original strength because it may stack solid and still not deliver the force.

[SteelShooten]

Follow-up on the mainspring with two coils removed:

Two is pretty much the limit without altering other parts. It will still set off Fed 100 primers but failed to set off about 1 in 18 Win WSP. An expedient shim brought the reliability back up to about 99%.

My splits came out consistently .1 sec shorter.

Some of my practice ammunition is loaded with Winchester primers. For that ammo, a mainspring that is 1-1/2 coils under factory length is probably -it-.

[ben b.]

Cutting coils of a compression spring decreases leverage in the compression (increasing force needed to compress for the same output), but also decreases pre-load.

Shimming (if I understand correctly) increases the pre-load on the spring.

Grinding the diameter down changes neither pre-load nor leverage, but decreases force of the spring, reducing compression.

If I have that all correct, it sure seems a tricky business cutting coils to reduce preload just to shim it back up to increase preload, all the while increasing needed compression. Reducing diameter seems like the way to go.

[Shadowrider]

Another thing you could do, provided you only shoot DA, is bob the hammer. I just looked at mine, and just guessing, I think you could easily get 150 grains of weight off of the hammer without going inside the profile of the frame. I bobbed the hammer on my 625 and got almost 100 grains of weight off of it (the 1st time. The 2nd time I chopped the whole back half off of it and reduced the weight to almost half of it's original weight). The Ruger hammer is much more robust so that's what I'm basing my guess on. This would allow you to go a bit lighter on the spring weight and reduce lock time too.