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Ruger hammer stop filing: how much is too much? (also, Super GP100 tuning log)


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I'm trying to get my Super GP100 to be a bit more tolerant of less-than-ideal primer depths and very slightly bent moon clips, without having to go back up the ladder in terms of hammer springs. One option of which I've heard is removing material from the stop at the top of the hammer, the bit which rests against the frame, so as to smack the transfer bar a little harder and push the firing pin a little further.

 

Before I got my 1/1000" calipers, I took a little material off, and the depth gauge says 0.071" from the hammer stop to the hammer face. How much further can I go? Obviously, it's a situation where taking too much off would be a giant pain and necessitate a replacement hammer.

Edited by Fishbreath
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1 hour ago, Fishbreath said:

I'm trying to get my Super GP100 to be a bit more tolerant of less-than-ideal primer depths and very slightly bent moon clips, without having to go back up the ladder in terms of hammer springs. One option of which I've heard is removing material from the stop at the top of the hammer, the bit which rests against the frame, so as to smack the transfer bar a little harder and push the firing pin a little further.

 

Before I got my 1/1000" calipers, I took a little material off, and the depth gauge says 0.071" from the hammer stop to the hammer face. How much further can I go? Obviously, it's a situation where taking too much off would be a giant pain and necessitate a replacement hammer.

I remember seeing a thread about doing this to a GP100 22 on the Ruger Forum. It includes pictures on how to make a jig to hold the hammer.

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This looks like the one. (edit: no instructions for hammer jig, but some good tips anyway.)

To reproduce some of the information here:

  • The original poster in that thread took 0.006" off of the hammer stop; more caused reset issues because of transfer bar pinching. (If I run into that, I've gone too far, but it seems like the kind of thing that could be salvaged by transfer bar/hammer face polishing.
  • I probably need to shim the cylinder for endshake reasons, although I won't know that for sure until my feeler gauges get here on Monday.
  • Bowen makes an extended firing pin I can try, which uses (or can use) shims to set protrusion.

Thanks for the pointer!

Edited by Fishbreath
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20 minutes ago, Fishbreath said:

This looks like the one. (edit: no instructions for hammer jig, but some good tips anyway.)

To reproduce some of the information here:

  • The original poster in that thread took 0.006" off of the hammer stop; more caused reset issues because of transfer bar pinching. (If I run into that, I've gone too far, but it seems like the kind of thing that could be salvaged by transfer bar/hammer face polishing.
  • I probably need to shim the cylinder for endshake reasons, although I won't know that for sure until my feeler gauges get here on Monday.
  • Bowen makes an extended firing pin I can try, which uses (or can use) shims to set protrusion.

Thanks for the pointer!

Check your messages.

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  • Fishbreath changed the title to Ruger hammer stop filing: how much is too much? (also, Super GP100 tuning log)

I decided not to build the jig and take a little more off by hand. Measuring between the two points in the picture (ignore the frame marks on the hammer, they're from a day when I didn't realize I'd missed a shim when putting the hammer back in), I went from 0.072" (my first measurement, after a bit of halfhearted filing prior to having a tool that could reliably measure 0.001") to 0.065". At 0.065", I can just start to feel the transfer bar binding at the start of the trigger reset, so I'm going to leave it at that.

 

Next thing on my list are more shims—I have a few coming from TriggerShims.com for the cylinder, the hammer dog, and the hammer (I know it's not touching the frame much, but I'd like to be sure it's not touching the frame at all).

PXL_20201018_163909969.jpg

Edited by Fishbreath
Fix hundredths->thousandths error
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Measurements today:

Cylinder gap is 0.0025" with the cylinder pushed forward, and 0.0075" with the cylinder pushed back. Headspace with fresh brass is correspondingly 0.0075" and 0.0025", for an endshake of 0.005". (Measuring between the back of the cylinder and the top of the recoil shield gives me the same figure.) I believe that's slightly out of spec, and my light strike and cylinder-binding issues suggest I should shim some of that out.

The hammer dog has 0.013" of play side to side. Lance at TriggerShims says I might be able to go down to 0.001"-0.002" if everything is oiled and polished, so I'll probably give that a try and see what comes of it.

With shims removed, the hammer had 0.016" of play. The factory shims are 0.006", so I'll replace them with a 0.006" and a 0.008" or so.

Shims are en route, so I can't speak to their effectiveness yet.

While I had things apart, I took the time to polish the mainspring strut and mainspring seat, all from 1000 grit to 2500 grit in 500-grit increments. On the mainspring strut, I hit the shoulder where the top of the spring rides and the ball that engages the hammer, along with the base where it passes through the seat. On the seat, I just did the top, where the base of the spring rides. Result: perceptible improvement in smoothness.

Edited by Fishbreath
Fixing thousandths/hundredths confusion again
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My TriggerShims shims came in today. I put in 0.005 shims around the hammer dog and 0.008 shims in around the hammer (in place of the factory 0.006 shims). The hammer has vastly less side-to-side play in it now, and I think the trigger pull is improved qualitatively. (The scale reads the same.)

 

Unfortunately, even the 0.002" endshake shim was too much—it prevented me from closing the cylinder at all. Oh well. At least I have them on hand if it changes over time, and with luck, the hammer shims and hammer stop changes will get me my reliable ignition.

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3 hours ago, Fishbreath said:

My TriggerShims shims came in today. I put in 0.005 shims around the hammer dog and 0.008 shims in around the hammer (in place of the factory 0.006 shims). The hammer has vastly less side-to-side play in it now, and I think the trigger pull is improved qualitatively. (The scale reads the same, about 7.5lb with a 10lb mainspring.)

 

Unfortunately, even the 0.002" endshake shim was too much—it prevented me from closing the cylinder at all. Oh well. At least I have them on hand if it changes over time, and with luck, the hammer shims and hammer stop changes will get me my reliable ignition.

 

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