Tuning a New GP100 10 shot .22

[DS-10-SPEED]

I have 3 617's and love using them in speed shooting sports, they have actions that are smooth and I have them set with moderate trigger pulls. I don't have a weak semi-auto trigger finger, I'm sure partly due to shooting DA revolvers for 40 years. For me a moderate trigger pull helps me keep the front sight on target, too light it's too easy to move off target and too strong it wiggles from finger tension.

 

My buddy bought a GP100 10 shot .22 and I made speed loaders for it. I finally decided to get one myself to see if it could be usable for pin shooting, NSSF and SCSA sports. As with any new .22 revolver the trigger pull is tough, really tough on the Ruger. I polished the action, added shims to prevent the hammer and trigger from rubbing on the frame. To get reliability with several brands of ammo I had to modify the firing pin (it came with a large flat pointed pin) and I milled 0.006" from the hammer stop to increase pin travel (can' t go any more without causing reset issues with a pinched transfer bar). I also had to file and polish a poorly machined ratchet on the cylinder that was causing 4 of the 10 to be very rough at the end of the DA pull causing slow spit times on those 4.

 

It's now pretty decent and I have it down to a 14lb hammer spring and an 8lb trigger return spring. A 13lb hammer spring feels really good (closer to my 617's) but I have 50% misfires. The only thing I see left is the massive heavy slow hammer and the energy robbing transfer bar. Has anyone tried the lighten the hammer and or transfer bar on a GP to increase firing pin speed? I only want to get a 1lb reduction, I like the 13lb hammer spring but can't use it.

 

I shot a 10 shot string for trigger speed comparison and it seems pretty smooth, just not as light as I want.

 

 

[Alaskan454]

I've tuned a few centerfire GPs and SRHs but never a rimfire.  Since you already maximized the firing pin protrusion I would check the endshake and headspace to make sure it's as tight as possible.  I'm not sure if the current GPs are press fit or screw in, but you might check and see if your firing pin could be replaced with one of these: http://parts.bowenclassicarms.com/index.php?main_page=product_info&cPath=8&products_id=49 

 

 

 

[DS-10-SPEED]

31 minutes ago, Alaskan454 said:

I've tuned a few centerfire GPs and SRHs but never a rimfire.  Since you already maximized the firing pin protrusion I would check the endshake and headspace to make sure it's as tight as possible.  I'm not sure if the current GPs are press fit or screw in, but you might check and see if your firing pin could be replaced with one of these: http://parts.bowenclassicarms.com/index.php?main_page=product_info&cPath=8&products_id=49 

 

 

 

Thanks for the input but that particular firing pin is not for the new screw in retainer, that is what I have. I don't see one listed there for mine. Maybe someone else has one.

Edited February 28, 2017 by DS-10-SPEED

[Alaskan454]

I figured that might be the case, what does the headspace look like? 

Edited February 28, 2017 by Alaskan454

[DS-10-SPEED]

1 hour ago, Alaskan454 said:

I figured that might be the case, what does the headspace look like? 

I've never checked for that before, how is that done? Do you add shims to the cylinder if the head space is too big?

 

Maybe a dumb question but since this is my first Ruger DA I think I should get at least one more.

 

Wouldn't the fact that it works fine with a 14lb spring and 5 brands of ammo from thick rimmed CCI to thin rimmed Winchester and getting a good rim indent say that the head space is good and the firing pin is long enough?

 

[Alaskan454]

I don't know much about different brands of .22 so I was just curious.  The headspace is how much room you have between the cylinder and the recoil shield.  Since you already made sure the firing pin had plenty of protrusion that's the next thing I'd check.  Based upon your pictures it's probably just fine though.  What I usually measure is the gap between brass rim and recoil shield. Take the ammo you plan to shoot in the gun and find the largest feeler gauge that will pass.  If you're tuning a competition gun you'll want it as tight as will allow reliable operation.

Edited March 1, 2017 by Alaskan454

[DS-10-SPEED]

I did some measuring and here is what I have.

 

Head space (with no ammo):

.011" max (cylinder pushed forward)

.007" min (cylinder pushed back)

 

CCI ammo sticks up about .001" (so max head space would be .010")

Federal ammo mostly flush to -.001" (so max head space would be .011" to .012")

Browning/Win ammo mostly -.002" (so max head space would be .013")

 

The recess in the cylinder for the cartridge rim is .039" +/- .0005".

 

The current firing pin sticks out about:

.030" with the transfer bar flush

.043" max travel if forced all the way in with a pin.

 

The minimum ammo dents could be .017" to .020":

.030" - .010" = .020"

.030" - .013" = .017"

 

So if I take worst case right now (.0385" + .007" - .043" = .0025") I have .0025" clearance before I could damage the cylinder if dry fired. Not much room for extending the firing pin or shimming the cylinder unless I have a longer firing pin with a thicker shoulder also to limit over travel (or just never dry fire).

 

If I new pin could be made with .005" added to the length and .005" added to the shoulder thickness it might work better and still not hit the cylinder if dry fired.

 

A new firing pin made that way would stick out about:

.035" with the transfer bar flush

.043" max travel if forced all the way in with a pin.

 

Anyway, It might not be worth the trouble and I should be happy having it work as good as it is.

 

Thanks for your help.

 

[DS-10-SPEED]

I decided to make this GP100 into another dot gun since I didn't like the sights that came on it. I had to make my own mount because I couldn't find one to fit a Burris FF3 the way I wanted.

 

Edited March 13, 2017 by DS-10-SPEED
Typo

[357454]

You have .004  end play in your Ruger, this needs to be minimized to .001 to .002. this will help with your ignition issue. I do not work on Rugers, however if this were a Smith you would have two options, stretch the crane or install spacers inside the cylinder. 

[DS-10-SPEED]

11 hours ago, 357454 said:

You have .004  end play in your Ruger, this needs to be minimized to .001 to .002. this will help with your ignition issue. I do not work on Rugers, however if this were a Smith you would have two options, stretch the crane or install spacers inside the cylinder. 

Thanks, I'll look into it.