S&W cylinder peening microscopic photos

[Griz]

My brother asked me to work on his 686 SSR that he uses for IDPA. He told me that it often fails to fire when he's trying to shoot fast. I assume that he is a victim of a gremlin named Skip Chambers, but I can't make it happen in dry fire.

There is some obvious cylinder notch peening. I remember a thread here where someone asked for photos of the "rebound peening" but I never saw any photos posted so I used a microscope to take some closeups to share here. Does this look bad enough to cause skipping? It was very hard to capture in a photo. The rebound peening looks much taller using my eyeballs looking through the stereo-microscope as opposed to taking a 2D photo.

Two chambers are timed very late. So late that when I pull the trigger, I feel a "clunk" an instant after the hammer falls. I assume that is the cylinder stop locking after the hammer fall.

I can also drag a finger on the cylinder and all chambers fail to lock before the hammer falls (but that happens on some of my revolvers that have never given any trouble so I don't put much weight on that test.)

Any advice on how to proceed? My preliminary plan of action is:

1) Fit a new cylinder stop (the old one is beat up pretty badly)

2) Fit a new hand to address the late timing

3) Erase the "rebound" peening with a cratex bit on a demel.

Should I also remove the primary peening, or should I try to peen it back into place, or just leave it as is? It seems risky to remove that metal as I'm sure it will get peened again and eventually there won't be enough metal left to hold the cylinder in the right position if I keep removing metal.

Edited April 26, 2015 by Griz

[Griz]

More pics

[toothguy]

Using a 1/8'' pin punch (hardened flat punch) you can gently tap the metal back into place. Once the cylinder stop gets an excessive flat spot it's not to hard to replace once you get the hang of the tricky spring. Do the cylinder stop replacement inside of a large zip lock bag so the spring won't get lost.

[Toolguy]

You want to put all the metal back where it came from. Use a flat ended punch for the straight side and the side of a 1/4 or 5/16 round bar for the ramp cut.

You can file a slight chamfer at the top of the right side of the cylinder stop to let it start going up sooner. Make sure you do the correct side (the one towards the ramp) or it will make things worse instead of better. This will help with peening and lockup.

Edited April 26, 2015 by Toolguy

[bountyhunter]

The curved area shown looks wierd. Makes me wonder if there is a problem with the cylinder stop. It should be peening a nice straight edge not curving. That is definitely where it is jumping the slot. I would fit a new stop and spring and see what gives after that.

[Toolguy]

It looks like just the top of the cylinder stop is hitting there. Sometimes people cut down the cylinder stop spring in an attempt to make the trigger return lighter. That will make the cylinder stop slower to pop back up in the slot in the cylinder. Just a guess, might not be the real problem.

[Griz]

The only people who have worked on it are me and S&W. I didn't do anything to the stop or spring... But I'm going to replace both.

Chamfering the trailing edge of the stop makes a lot of sense to me.

I think everyone is telling me to fix the stop and deal with the cylinder peening first and then see where it is timing-wise before I replace the hand.

[seanc]

The cyl stop in my 929 is sloped.

One of my 627's used to need a new cyl stop every 10k clicks or so. When it got the new style stop, it hasn't skipped yet and it has a clipped stop spring and a 3.75 action that pops winchesters 99%.

I had a new ti cyl fitted to a 625 and that gun started skipping in less than 10k. The cyl was not visibly damaged, it went back to the smith who identified peening on the scalloped side. It was not visible but you could feel it. The ledge was knocked off with a cratex bit and the gun never skipped again, but its also now in the museum....

edit...the point is, check both sides of the notch. Repair the one side by hammering it back and touch the other side to make sure there isn't a bump there that is constributing to the jump.

Edited April 28, 2015 by seanc

[Griz]

The cyl stop in my 929 is sloped.

Sloped on the trailing edge like Warren suggested?

edit...the point is, check both sides of the notch. Repair the one side by hammering it back and touch the other side to make sure there isn't a bump there that is constributing to the jump.

I posted those microscopic photos to try to document for the forum what that bump looks like and how subtle it is... It is hard to see with the naked eye on my example.

As I understand it, the peening at the end of the ball cut (what I called "rebound" peening) is the cause of the chamber skipping and the nasty looking peening on the "impact" side of the notch seems to be the effect of the stop jumping the rebound peening and hitting the impact surface very high.

[seanc]

The cyl stop in my 929 is sloped.

Sloped on the trailing edge like Warren suggested?

edit...the point is, check both sides of the notch. Repair the one side by hammering it back and touch the other side to make sure there isn't a bump there that is constributing to the jump.

I posted those microscopic photos to try to document for the forum what that bump looks like and how subtle it is... It is hard to see with the naked eye on my example.

As I understand it, the peening at the end of the ball cut (what I called "rebound" peening) is the cause of the chamber skipping and the nasty looking peening on the "impact" side of the notch seems to be the effect of the stop jumping the rebound peening and hitting the impact surface very high.

your understanding is same as mine. This is what the cylinder stop slope looks like, it is pronounced...

Edited April 28, 2015 by seanc

[seanc]

And this is a sample of my 627, scallop side (ball cut) peening.

[buckjk]

Interesting pictures. So would any of you recommend proactively beveling the cylinder stop trailing edge on a new 625 to add longevity to the cylinder? Is there anything else that could be done to give the cylinder a fighting chance under heavy DA use, or is it just something to fix if and when it happens?

[Toolguy]

I would do it at the beginning. I believe it will add life to the cylinder and stop. The old cylinder stops were angled like the one in post #10. This makes a lot of sense because it allows the leading edge of the stop to engage more surface area in the cylinder notch.

Also, the old hands were flat on top like the Power Custom wide replacement hands. The flat top makes the cylinder turn easier at the start of the trigger pull. I think they lost some things along the way that the old timers used to know.

Edited April 30, 2015 by Toolguy

[Ty Hamby]

Others have stated most of this. I want to reenforce what I have learned on several Ti cylinders.

Skipping chamber is mostly caused from the ski jump at the bottom of the ehtry slope into the cylinder notch. This peen is usually not visible and a quick hit with cratex will solve your woes. When you stop the cylinder stop from jumping the gap (notch) you fix the large peen-ing on the opposite side. Any "ski jump" located at the bottom of the cylinder notch entry slope causes the stop to hit high in the notch. Continued high hits peen as seen above and eventually miss the notch altogether.

[Bosshoss]

The latest manufactured guns I have had come into the shop have had the new style cylinder stop that has a angled ball top.

I have been ordering cylinder stops straight from S&W and getting the new style.

Still lots of the old style flat top one out there. That is still what I get from Brownell's.

Will be glad when the old style ones get out of the system.