Narrowing cylinder stop to get bore/chamber alignment

[My Toy]

Of the 30 some revolvers I own (mostly S&W, Ruger and Colt) I've only had two that there was either improper machining of bolt notches on the cylinder or cylinder stop cut out in frame and you could not get enough rotation of the cylinder to get proper bore/chamber alignment as checked with a range rod.
On these two revolvers it took excessive pressure with my fingers turning the cylinder against the cylinder stop (way more effort than could be exerted by the gun's hand or pawl) to get the range rod to pass in to most of the chambers.
I experienced this on a GP-100 several years ago and made a jig to stone off a couple of thousandths of an inch while keeping the sides of the stop parallel and square. This worked beautifully and that revolver would not only pass a std. range rod but also a match range rod.
I recently had the same experience with a Smith 686-6. I removed about 4 thousandths from the cylinder engaging surface of the stop, fitted an oversized hand and all the chambers will pass a match range rod. The gun displays great accuracy which I'm sure was contributed to by proper bore chamber alignment.
My only concern is that I'm sure that the cylinder stop is a MIMed part and I wonder if I compromised the strength of this part. The cylinder stop didn't stone easily it seemed pretty hard so I don't know if long term peening of this part will be an issue.
Anybody else try this? What was your long term experience?

 

[Hapworth]

I'm not a MIM expert, but I believe you're in the clear because MIM parts are of equal hardness all the way through, unlike forged which could be compromised by stoning because those parts are harder toward the surface, but softer inward.

 

[My Toy]

I'm not a MIM expert, but I believe you're in the clear because MIM parts are of equal hardness all the way through, unlike forged which could be compromised by stoning because those parts are harder toward the surface, but softer inward.

That was kind of my thought too. I'm pretty sure that some parts that are in extreme working contact like trigger sears and hammer notches are surface hardened for long life. And I'm pretty sure the hardening doesn't go very deep (maybe a couple of thousandths). But there are other revolver parts that are routinely filed/stoned for fitting like ratchet pads and hands that are probably in more stressful contact than a cylinder notch and cylinder stop and I'm sure that these parts are not surface hardened.
I'm no metallurgic expert either; maybe someone with true experience in this field will chime in.

 

[cmj8591]

If the gun is not locking up when you cock it, the problem is either the hand or the ratchets or some combination of those two things. The stop would not cause the gun not to cycle up. Mim parts do have a hardened surface and it is possible to file or stone through it. It is about as deep as the hardening on conventional parts.

 

[My Toy]

If the gun is not locking up when you cock it, the problem is either the hand or the ratchets or some combination of those two things. The stop would not cause the gun not to cycle up. Mim parts do have a hardened surface and it is possible to file or stone through it. It is about as deep as the hardening on conventional parts.

I know the gun is not locked up when you cock it; it should be locked up when you pull the trigger and before the hammer falls. This revolver does lock up; the problem is that when locked up the bore and several of the chambers are not in alignment as checked with a range rod. When you check bore/chamber alignment with a range rod the revolver is in a locked condition as if the instant before it would drop the hammer. The gun is inverted so the barrel is vertical the hammer held back and the trigger pulled all the way back to rotate the cylinder to it's maximum rotation given the combination of parts (hand, ratchet, cyl stop, etc.) in the gun. A range rod should pass easily in to each chamber.
Problem is the cylinder stop is restricting the cylinder from rotating enough to align the several of the chambers.
I know it is the cylinder stop because when performing the range rod test (with the hammer removed since I don't have a third hand to hold it back- and it really doesn't effect rotation) the cylinder can't be rotated enough with my fingers (at least reasonable tension) to allow the range rod to enter the chambers in question without "ticking" on the chamber mouths.
So it seems to me that either there is a couple of the cylinder notches that were machined slightly off or the opening in the frame for the cylinder stop is slightly off. I'm guessing it is the cylinder notch thing.
Instead of trying to adjust the notches in the cylinder or opening up the cylinder stop hole in the right direction the most prudent thing was to try to narrow the cylinder stop several thousandths (since it is the least costly of parts to work on in the event of a screw-up). It worked beautifully except for my question about compromising the integrity of the cylinder stop.
As a side note the gun just came back from Smith and Wesson after a 3 month visit there to correct excessive end shake. They supposedly checked over the entire gun for function but I'd be willing to bet a range rod test is not part of the checkout. The gun carried up and fired and was safe and that was probably the extent of their concern.
I'm guessing based on S&W's check out and returning a production revolver to a customer with it's function check as OK, correcting this problem would fall under the category of custom tuning.
I've got a number of other Smiths that I bought new and used that easily pass the range rod test (even some of their J-frames).
This particular gun is just a problem child.
If anyone knows of a better fix than I tried, please I'd like to hear from you.

 

[My Toy]

I did some research on MIMed parts today and came across a
piece written by an engineer at S&W on the topic. I can't remember what forum I came across this info on (I think it was the 1911 forum and I can't remember the S&W reps name--if anyone is interested I could probably find it).
Anyway he described the process for making the parts and the reasons for going to MIMed parts. The piece was really in answer to the wide spread belief that MIMed parts are inferior to comparable forged parts.
As far as I was interested though he confirmed that MIMed parts are basically of consistent hardness throughout and are selectively hardened after they are made depending on the application of the part. Mainly of discussion were sears and triggers which he said are the parts that probably undergo the most stress and are in need of greater degree of hardness.
Now back to my narrowing of a MIMed cylinder stop to get a little more rotation of the revolver's cylinder. I'm not sure what degree of hardening is applied to this part if much at all.
Since I actually did this and it is not theoretical I tried a limited test where I install only the rebound slide to power the trigger so I could simulate double action firing of the revolver without having to use snap caps. With nothing better to do today I dry fired 2000 double action trigger pulls with the cylinder banging in to the cylinder stop as under actual firing conditions.
Ever 500 trigger pulls I examined the cylinder stop where I removed several thousandths of a inch where the cylinder notch meets the stop. Looking at it under magnification the only change in the cylinder stop after 2000 impacts by the cylinder notch was a slight polishing of the contact area. No evidence of wear or peening (actually the only peening was what you commonly find at the top edge of the cylinder notch).
Based on this I'm not to worried about the amount of material I removed from the contact side of the cylinder stop.
Any thoughts on this?

 

[ms]

Have you tried the range-rod test with the trigger forward? Results?

 

[My Toy]

Have you tried the range-rod test with the trigger forward? Results?

ms:
Yes I tried the range rod test with the trigger at rest (although the test requires that the trigger be pulled all the way back with the hand rotating the cylinder to the max) and the range rod wouldn't entry two additional chambers without "ticking" on the chamber mouth.
With the four thousandths I removed from the cylinder stop, the cylinder has enough additional rotation and functions beautifully and passes a match range rod in all chambers.
I called Brownells and talked to one of their gunsmiths about the material I took off of the MIMed cylinder stop and the 2000 trigger pull test I tried and in his opinion he didn't think I seriously compromised the part. His advice was to just keep any eye on it. Or if it failed try a Power Custom oversized cylinder stop which he said was made of tool steel and that oversized parts are intended to be fitted by filing or stoning.