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Discussion Starter #1
@Iowegan

(Since Iowegan seems to be quite an expert on the topic of GP100 and S&W endshake, I'm hoping I can tempt him to answer this question):

Background: About a month ago, I purchased a brand new GP100 Match Champion chambered in 10mm. The revolver required an immediate trip back to the factory due to a broken firing pin and cases jamming in the cylinder (the latter issue turned out to be ammo related...stay away from Armscore 180gr 10mm if you're shooting a 10mm revolver!). However, the revolver was returned to me with a new cylinder installed, due to the fact that the technician tested several new cylinders before he concluded that the Armscore ammo was at fault and simply decided to leave the last one on prior to shipping the gun back to me. When I received my revolver back from repair, I noticed that the endshake had opened up a bit (probably due to the new cylinder): the gun now exhibits an endshake of about .0035" or .004" with a B/C gap of roughly 0.0065" (i.e. a "pushed forward" gap of .003" and a "pushed backward" gap of .0065").

Now: I've read many of Iowegan's posts regarding Ruger DA revolver endshake, and I fully appreciate that the degree of endshake that my gun exhibits is probably perfectly acceptable (I understand the spec is .002" to .005" or so). Be that as it may: The perfectionist in me wants to get this value down as low as possible, and the avid tinkerer in me is excited to take the gun apart anyways, so I went ahead and ordered a cylinder shim kit. Now on to my questions (finally):

  1. What is the justification for how high the LOWER END of the GP100 endshake spec (0.002") is as compared to the LOWER END of a S&W 686 endshake spec (0.0005", or effectively 0)? It seems to me that the lower end of the spec should be governed by mechanical considerations that apply equally to both revolvers (thermal expansion of metal, variation in head spacing due to ammo variability, etc.). So why would the S&W's be so much lower?
  2. [NOTE: The answer to this question depends largely on the answer to the above question] - Since I will be tuning my endshake anyways, what final endshake value should I shoot for? Would it be prudent to leave 0.001" of endshake? Should I leave more? Or should I just go for broke and try to get 0.000"? What is the "ideal" value for a GP100?
  3. All of what I have read regarding GP100 endshake has been in the context of the 38/357 chambering. Are there special endshake-related considerations for the 10mm caliber? For example, a couple things occured to me:
    • The 10mm cartridge is rimless and headspaces off the case mouth, which contacts a bearing surface (i.e. a little "shelf") near the end of the cylinder bore. This means the overall headspace of a given cartridge is dependent on the total case length of the cartridge, rather than simply the thickness of the rim as would be the case for a rimmed cartridge (38/357). This dimension (the total case length) may have a tighter (or looser) tolerance than the rim thickness of a rimmed cartridge. If this tolerance is LOOSER, it might make since that a 10mm GP100 would require a LOOSER endshake value to accommodate the variability in headspacing; if this tolerance is TIGHTER, then the opposite would be the case. Thoughts?
    • I would like to purchase an aftermarket moonclip which will allow me to fire 40 S&W from this revolver. In this case, the thicker moonclip would effectively headspace the 40 S&W case off the back end of the cylinder. Perhaps it would be advisable to leave a little endshake to allow for the fact that this headspace value will likely differ from the 10mm headspace value?
  4. Lastly (and I'm kinda thinking out loud here): Maybe cylinder endshake and headspacing are totally unrelated, and my underlying assumption that endshake can help accommodate headspacing variability is just plain wrong? My assumption was that a zero endshake scenario could result in a situation where a "slightly long" cartridge jams against the recoil shield.

Anyway, any and all responses are welcome! I'd especially love to hear from people who have actually performed cylinder shimming on their revolvers and have seen the results in action. And, of course, Iowegan's input is always welcome!
 

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taters613, My opinion …. you're probably over thinking the situation!

To me, a perfect endshake for a GP100 would be no less than .002" and no more than .003", about in the middle of the max spec of .005". Reason? GP100 cylinders are notorious for binding up when endshake is tighter than .002". So, your gun is very close to optimum. S&W revolvers are made to much tighter specs so they can deal with endshake as tight as .0005" without binding. BTW, most of the binding comes from burnt powder residue. S&W has a deflector on the yoke to prevent crud from getting into the yoke tube and behind the ejector.

The goal for fitting a cylinder to a frame is to have endshake, B/C gap, and headspace all within specs. There are 5 measurements that affect the final fit …. how much barrel protrudes from inside the frame, the length of cylinder body, the length of the ratchet column, the length of the yoke tube, and finally, the depth of the center hole in the cylinder. Any time you change one of the measurements by installing shims or filing metal, likely you will make one measurement better and another one worse.

I really don't have any experience with 10mm Auto chambered GP100s. I do know they function the same as a 45 ACP, 40 S&W, or 9mm when it comes to head spacing on the case mouth. You are at the mercy of the ammo manufacturers unless you reload and even then it's hard to find cases that measure at the SAAMI optimum length of .992", which is the length used by Ruger to set headspace. Keep in mind, excessive headspace can come from a short ratchet column on the rear, from a short yoke tube in the cylinder's center hole, or just from short cases. You can determine headspace and figure out where any excess is coming from by chambering a sized .992" long case in the cylinder then indexing it under the firing pin. Measure the distance from the case head to the recoil shield with the cylinder held back, using gap gauge blades. It should be about .010" and no more than .015" with the cylinder held forward. Installing a shim in the cylinder's center hole will decrease headspace along with endshake. If "held back" headspace is less than .010", I definitely would not install a shim (endshake bearing), however if "held forward" headspace exceeds .015". I would install an endshake bearing because excessive headspace can result in misfires.

You are fortunate that your gun is new because with guns that have been fired quite a bit, the yoke tube will cut a channel inside the cylinder center hole. This becomes obvious if you measure a .006" endshake then use 2ea ,002" endshake bearing to correct it to .002". When there is a channel in the center hole, likely just one .002" endshake bearing will bind up the cylinder. This means you have to use a special grinding bit to remove the channel from inside the center hole. Once it has been flattened, endshake bearings will correct excessive endshake.
 

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I experimented with cylinder shims on one of my Rugers when it was new. It had about .008 endshake and when held forward, the cylinder would hit the back of the barrel. I shimmed it to .001 and the cylinder would bind when trying to swing it out sometimes and sometimes it would bind when trying to rotate the cylinder. I reshimmed it to .002 with a different combination of shims and it would still bind sometimes. I then reshimmed it to .003, which gave me a .004 B/C gap, and I have never had a problem since. I now have over 20K rounds through that gun and have had no problems whatsoever.
 

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Discussion Starter #5
Thanks for the great feedback guys.
Iowegan: I took your advice and measured the headspace for all six cylinder positions using a spent casing I had lying around. Prior to measuring the headspacing, I used a pair of calipers to measure the length of all the spent casings I had: to my surprise, they all measured around 0.980", which is a full 0.012" shorter than the nominal! This was the case for two different brands (Herter's and Armscore), and the case length for unfired rounds seemed to be right around the same length. I can't imagine why two different ammo makers would use cases with lengths that were this far off from spec. Any guesses?
So I grabbed a case which I had measured as having a length of right around 0.979" or 0.980" and used it to measure the headspace in the way you suggested. I ended out getting between 0.020" or 0.021" for every cylinder position. These measurements were all taken with the cylinder held back, so presumably the "cylinder forward" measurements would be larger by about 0.0035" or 0.004", since this is the endshake I've measured on my revolver. These measurements seem consistent with what you said: The difference in case length from the spec (-0.012") almost perfectly accounts for the larger headspace I measured compared to what you quoted (+0.0105" or so above the nominal 0.010").
This is making me lean towards experimenting with the shims (and it doesn't help that I've already ordered the shims and cylinder disassembly tool :p). If ammo manufacturers are consistently using 10mm cases that are shorter than spec, and my GP100 headspaces according to SAAMI spec, then tightening up the endshake might help prevent the possibility of light primer strikes on the shorter cases, right?
Notathome: Thanks so much for your input. I think I'll take a similar strategy to yours: tighten up the endshake to 0.001" or 0.002", see if I have problems, then loosen it up if I do. And I'll make sure to keep this thread updated with my progress.
Thanks again guys!
 

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Discussion Starter #6
So I've got a related follow-up question: When I received my revolver back from its initial warranty repair, I noticed that the cylinder rotational play had dramatically increased (that is, the amount that the cylinder can be rotated with the trigger held back). Prior to the repair, the rotational play was essentially undetectable; after the repair, it was looser than I've felt on any other gp100 (I've owned two and shot many). It I had to guess, I would estimate the rotational play at around .010" of lateral movement, measured at the outer edge of the cylinder. My assumption is that this condition was caused when they replaced the cylinder, but did not refit the revolver with a new cylinder latch. The existing latch was clearly fitted to the original cylinder (you can see the filing on the right side of the latch), and the new cylinder must have wider cylinder notches.
So, a couple questions here:
1) How much rotational play is TOO much?
2) Should I consider ordering a couple cylinder stops from Midway and trying to fit a new one myself? The process seems pretty straightforward: file the outside edge until the cylinder stop fits snugly into the tightest notch on the cylinder. Plus, the cylinder stops can be had for only $3.69 on Midway, and I think I'd enjoy the project.
3) If I DO try to fit a new latch to my revolver, should I aim for leaving a small amount of rotational play? Are there any tricks that I should know about in terms of the fitting process?
All feedback and thoughts are welcome, but ESPECIALLY from those of you who have actually gone through the process of fitting a new cylinder latch!
 

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I have fitted a new cylinder latch once before. It is not so much that the latch fits in the grove in the cylinder as much as do the bores of the cylinder line up with the bore of the barrel. This is actually a little difficult to measure without special tools. The cylinder needs to be able to rotate enough so that the bullet can align the cylinder bore with the barrel bore as it goes into the forcing cone.
 

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I agree with notathome. I would think the play is a function not only of the cylinder stop but the pawl as after rotating the cylinder the pawl slides up the side of the ratchet and prevents rotation in the opposite direction to a degree. Only guns I am aware that hold the cylinder tight when firing are old style Colts.
 

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taters613, On a newer revolver, cylinder side play does NOT come from a cylinder latch loose fit in the lock notches …. rather it come from the widow in the frame being larger that the width of the cylinder latch. You can get yourself in big trouble if you try to fix side play without the proper tools because you can end up with a cylinder-to-bore alignment issue.

I used to make and sell precision brass range rods, which are used to determine cylinder-to-bore alignment and to measure side play. Below is a photo showing range rods from 22 Mag on top, 22 LR in the middle, and centerfire at the bottom with a variety of caliber specific heads and calibrated cases. Although range rods have been used for many decades, they have now been replaced by electronics technology in the form of a miniature camera on a flex shaft called a "borescope" or an "endoscope". I finally broke down and bought a cheap endoscope that plugs into the USB port in my laptop. I found I can actually see when the cylinder aligns with the bore and I can see any fouling or other defects in the bore …. a truly great tool for about 20 bucks. Here's a link: https://www.amazon.com/dp/B07FPB3HG4/ref=dp_cerb_2

I don't know what Ruger uses for a cylinder side play specification but general gun smith specs are +or- .005". Almost always, the cylinder will have considerably more play in one direction than the other but not more than .005" in either direction. The key is to have perfect cylinder-to-bore alignment when the hammer is fully forward with the trigger pulled …. the same condition as when the gun is being fired.

Personally, with the issues you have mentioned, I would send the gun back to Ruger and have them fit a new cylinder and correct the problems.

 

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Discussion Starter #10
Thanks again for the advice Iowegan!
After writing my previous post, I did some experiments and basically realized the exact fact you pointed out: It's more the cylinder latch that is shifting around in the window than it is the cylinder moving around on the cylinder latch. I proved this to myself by gently pressing the cylinder latch inwards so that it was biased against the inside edge of the window, and then trying to rotate the cylinder. In this case, there was less than half the amount of rotational play than there is normally. So maybe my conclusion was wrong...maybe they DID fit a new latch, and they did so incorrectly. I would definitely estimate the rotational play to be in excess of 0.010" (or greater than 0.005" in either direction).
In any case, I took your advice and shipped the revolver back to Ruger. I was a little conflicted about whether or not to do this, since I'm somewhat concerned that their response will be "It's all in spec" or something along those lines. However, the factor that tipped the balance was actually that I lost the rear sight windage spring last night while swapping out the rear sight blade :p. They agreed to replace this at no charge, and to just install a brand new sight blade so that I can keep the original as a spare.
I also just ordered one of those bore scopes you recommended. I had no idea these could be had at such a low cost! How cool! I can think of countless uses for one of these things even outside the world of firearms.
Anyway, I'll write up a post when I hear back from Ruger. I'm cautiously optimistic, since I've never had anything but excellent experiences with Ruger customer service.
 

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Discussion Starter #11
Update:
So I just got a call from Brian, the gunsmith at Ruger who’s working on my gp100, and I believe this is the same gunsmith who worked on my gun the first time around. So far this is looking like another excellent experience with Ruger customer service!
He agreed that a new cylinder latch was called for, and also that the endshake was slightly excessive. When I asked him what endshake value he generally aimed for, he said right around .004”, and that mine was measuring at around .0055” or so, which he described as “just barely out of spec”. He went on to explain the mechanical justifications for the endshake specs (basically exactly the same info as what the folks around here have explained). He then asked ME what endshake value I would prefer, which honestly blew my mind. I told him that I’ve preferred my guns tighter in the past, but that I would defer to his judgement since he’s the expert.
In the end, he said he will be replacing the cylinder latch and crane assembly, and possibly the cylinder as well if it proves necessary, and that he would throw on a new rear sight blade. He said the gun should ship out tomorrow afternoon and hopefully be back in my hands by Friday, which is a 9 day turnaround door-to-door. He then asked me what size T-Shirt I wore, and said he would throw in a Ruger T as well as a couple silicon gun rags for my trouble!
Honestly every experience I’ve had with Ruger customer service has been simply outstanding, and this experience is looking to be the best (although I am of course reserving my final judgement until I see the gun itself!). It seems that they really take accountability for their mistakes, and go above and beyond in order to satisfy their customers. In this case, I sensed that the gunsmith/technician himself was taking accountability for the mistakes he made during the first repair and trying to provide a higher level of service (along with some free swag!) in order to account for it, which I think reflects the strong culture of accountability at the company as a whole.
For anyone sending any firearm in for repair: I would HIGHLY recommend adding a note to the repair instructions stating “have service technician call me before any work is performed!”. So far, every time I’ve done that I’ve received a call from the gunsmith, and it’s always lead to an informative and valuable conversation. They also seem open to accepting input from the customer (e.g. how much endshake do YOU want?).
 

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Discussion Starter #12
Update:
My revolver arrived back from repair on Friday, which equated to a nine day turn around door-to-door. Not bad. The packing slip indicates that a new crane was fit, along with a new cylinder latch and pawl. A new rear sight blade was also installed.
Upon inspection, I found that the endshake had been reduced dramatically: Whereas it was about .0045" or .005" before, it is now somewhere in the neighborhood of .001" (definitely no more than .002", and possibly .0015"). The "held forward" C/B gap is a tiny bit over .006", and the "held backwards" gap is definitely no more than .0075" (unfortunately I lost one of my gap measures so I can't measure .007" :p). I am slightly concerned that this might be TOO tight, and that the cylinder will lockup when things get a little hot/dirty; we'll just have to wait and see. I'm not completely confident in my endshake measuring techniques, so it's possible that my measurements are off.
Additionally, the rotational play when in full lockup appears to be greatly reduced. There is still a little "jiggle" of maybe a couple thousands, but it's much more in line with what I'm used to seeing from a GP100. The rotational play seems consistent between cylinder positions as well. I inspected the new cylinder latch and, sure enough, this one is held firmly within the window in the frame, whereas the old cylinder latch had a whole bunch of side-to-side play within the window.
I took @Iowegans advice and purchased the bore scope linked above for about $24 or so on Amazon. I would highly recommend this borescope to anyone; it's super easy and fun to use, and the camera resolution, while not great, is perfectly adequate for most tasks. It makes checked the cylinder to bore alignment extremely easy, and I've already used it on every one of my other firearms just for kicks. I was able to use this device to check the cylinder to bore alignment, which looked fine as far as I could tell. Half of the cylinder bores where slightly misaligned in the upwards direction (i.e. I could see a tiny bit more of the cylinder face on the bottom side than I could the top side), but for every one of the cylinder bores I was able to see the full boundary of the hole in the cylinder while looking down the bore with the borescope. The other half of the cylinder bores appeared perfectly aligned.
Finally: Not only did Bryan at Ruger throw in a Ruger T-Shirt, but he also threw in six extra moon clips for my revolver. What a class act!
I'll post another (hopefully final) updated after I actually get out and shoot this thing. Hopefully that will be in the next few days.
 

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I love it when a plan comes together. Glad you sent your gun to Ruger …. now it's the way it should be. Not to worry about the endshake being too tight …. it never wears tighter but it will get a bit looser. Meantime, take a tooth brush with you when you go to the range. If the cylinder starts binding up, swing the cylinder out, press the ejector rod all the way in, then scrub the back side of the star wheel and ejector shaft to remove any residue. Just one flake of unburned Unique powder is enough to bind up a cylinder.
 

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amazing!

Wow, what a great thing to read just after I bought my first Ruger revolver!

No problems with my Super Redhawk 10mm yet, but it's good to know Ruger will take care of business.

Today's S&W would have been unable to understand the issue, sent OP a bill for warranty work, and possibly damaged his firearm in the process.
 

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Discussion Starter #15
It is really quite remarkable. I’ve had nothing but excellent experiences with Ruger customer service, and I certainly cannot say the same for S&W. I’ve only had one warranty return experience with S&W and, while it wasn’t a complete failure, I would say they did the “bare minimum” to address the very serious problem I identified with the revolver in question (failure to carry up), and flatly refused to perform work that they deemed unnecessary based on their limited specifications (badly clocked barrel). All my experiences with Ruger have been exactly the opposite. They really do seem to be head and shoulders above the competition in this respect.
And to clarify: I mean this more as a compliment to Ruger customer service than as a slight to S&W’s.
 

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It is really quite remarkable. I’ve had nothing but excellent experiences with Ruger customer service, and I certainly cannot say the same for S&W. I’ve only had one warranty return experience with S&W and, while it wasn’t a complete failure, I would say they did the “bare minimum” to address the very serious problem I identified with the revolver in question (failure to carry up), and flatly refused to perform work that they deemed unnecessary based on their limited specifications (badly clocked barrel). All my experiences with Ruger have been exactly the opposite. They really do seem to be head and shoulders above the competition in this respect.
And to clarify: I mean this more as a compliment to Ruger customer service than as a slight to S&W’s.
The stories about Ruger’s excellent customer service are legion. Smith and other gun makers would do well to emulate Ruger.
 

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The stories about Ruger’s excellent customer service are legion. Smith and other gun makers would do well to emulate Ruger.
Hey, I'd settle for the Smith and Wesson of 2 years ago, let alone matching Ruger CS.

2 years ago was when S&W replaced the slide on my M&P pistol, which had cracked. They paid shipping in all directions, didn't cost me anything but time.

I had put maybe 10k rounds through the gun and owned it for at least 5 years. But they replaced it "at no charge," per their lifetime service policy.

Then you have the S&W of 2019, who claimed a broken trigger stud in a 610 was "normal wear and tear," and tried to charge me to fix it.

They also broke it completely before sending it back, then denied having done so.

FWIW, I checked my 10mm Super Redhawk. It has VERY little endshake. Almost none. It's tight! This pleases me.
 

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Discussion Starter #18
FINAL UPDATE (hopefully): Finally got this gun to the range, and it shot great! Put 30 or so rounds of Sig 180 grain FMJ 10mm through it with no problems whatsoever. Accuracy was excellent until I turned into a flinch-o-matic at the end 😉. No problems with extraction; even without the moon clips, the spent cases would basically slide right out when I turned the cylinder vertically.
Also, I put a dozen rounds of cheap 40 s&w through it without any misfires! I’m really excited about this, because many folks have seen light primer strikes shooting 40 in 10mm Ruger revolvers and have been forced to fork out $70 (plus extra for the extraction tool) to get the TK custom moonclips which cause the 40 rounds to headspace correctly. But the primers looked very well struck when they came out of my gun, so maybe I just got lucky 😄. One thing I did notice is that, following my range trip, this gun was MUCH dirtier than my other revolver (colt model 3-5-7), and I wonder if this has to do with the larger B-C gap (about .0065” on the ruger, and about .002” on the Colt). There was a particularly large amount of carbon on the bottom side of the top strap, just above the forcing cone. Is this typical? I’m not a “clean freak” by any means, so I don’t mind much either way.
So: while it may have taken two trips back to the mothership, I am now extremely happy with this gun. Plus I got a bunch of free moonclips, a T-Shirt and some priceless knowledge and education out of the experience, so I can safely say that I will continue to be a devoted Ruger fanboy. Thanks for all the help guys!
 

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Yeah, I'm a little skeptical that the extra-thick TK Custom .40 S&W moon clips are an absolute necessity. If they weren't ~$8 each, I'd probably get some "just in case." But, here we are.

I'll find out for sure next range trip. Planning to put 100 or so rounds of .40 S&W through my Super Redhawk, using my old S&W 610 moon clips. If they all go off, I'll consider it problem solved.

For more relevant testing, I should also try 100+ .40 S&W's using the Ranch Products Super Redhawk-specific moon clips I just got.

Darn, more shooting required! Such a burden! :)
 
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