Replacing the cylinder stop spring

[acl864]

After reading the original posters explanation of the issue. I'm wondering if the recoil isn't causing a 'short stroke" on the trigger. That would explain the functioning issues and I've seen that happen before on DA guns with hyper recoil.

 

[Hondo44]

It's looking to me like the distance between the lower rear of the cylinder stop and the opening of the hole in the frame is maximum whenever the ball of cylinder stop is all the way up in the frame. And this occurs both when the trigger is fully released, and when the trigger is pulled far enough for the trigger to flick down out of the cylinder stop slot. If so, I think I can just leave the trigger and hammer in their rest positions. That should give me the most room to extract and remove the spring, and insert the new spring.

You're exactly right.

 

[Mike_Fontenot]

I just got back from the range (and I haven't done the spring replacement yet), and it DID show that the problem IS correlated with the power of the round, although not to the degree that I had expected. The full-spec Underwood 240gr had the problem on the very first shot. Then, I shot two sets of 5 rounds of Black Hills (about mid-range .44mag), and expected no failures, but got 1 failure out of the 10. Next, I shot 3 sets of 5 rounds of S&B (about at the bottom of .44mag), and got 1 failure out of the 15. Finally, I shot 4 sets of 5 rounds of Georgia Arms (really about mid-way between the bottom of true .44mag and the top of the .44 Special+P range). I got no failures out of the 20.

After Thanksgiving, I'll put in the stiffer spring and see if I still get any failures with the UW 240gr ammo. If I do, that will tell me that there is some other problem. If not, I'll be done.

 

[Mike_Fontenot]

After reading the original posters explanation of the issue. I'm wondering if the recoil isn't causing a 'short stroke" on the trigger. That would explain the functioning issues and I've seen that happen before on DA guns with hyper recoil.

Thanks for that tip. If the problem doesn't go away after I put in the stiffer cylinder stop spring, that may point to the possible cause you've brought up, or maybe to something else. I HAVE previously put in the lightest possible trigger rebound spring, in order to get the 2-1/2 lb SA trigger pull I wanted. I also put in a lighter mainspring, just heavy enough to prevent any light strikes. The DA pull is still not extremely light ... probably about 9 lbs.

I've done the same SA trigger-pull modifications on my 686 .357mag, in order to get the same trigger pull as on my 69 .44mag. I've shot that gun a lot with full power Underwood 158gr ammo, without this problem currently happening. But a while back, I did get an even more drastic failure on that gun, where the cylinder stop quit working at all, and just left the cylinder to rotate constantly, even after multiple cocks of the hammer. I sent it to S&W, and they said they replaced the trigger stud. It's been shooting fine since.

 

[Hondo44]

Push in on the frame mounted firing pin from the rear to inspect the tip. Does it look like it extends long enough and is it properly shaped?

 

[Mike_Fontenot]

I'm wondering if the recoil isn't causing a 'short stroke" on the trigger. That would explain the functioning issues and I've seen that happen before on DA guns with hyper recoil.

I think there is evidence that "short stroking" of the trigger can't be the cause of my problem. When the cylinder rotates after the shot, the firing pin is leaving a trail scratched on the back of the brass. The firing pin doesn't retract until the trigger is released. And after the firing pin retracts, it doesn't again protrude until the hammer is fully cocked, released, and hitting the firing pin. So the rotating of the cylinder is happening BEFORE the trigger is released after the shot.

 

[Mike_Fontenot]

Push in on the frame mounted firing pin from the rear to inspect the tip. Does it look like it extends long enough and is it properly shaped?

Yeah, it looks fine.

 

[WR Moore]

After noting that your problem only exists with a specific boutique load, I'd strongly suggest you simply don't use that ammunition any more.

I've never used Underwood, and only recently heard of them and have nothing personally against them, but I long ago watched several firearms destroyed by loads from various boutique ammo makers that promised exceptional velocities at SAAMI pressures. They were half right. A few foot seconds isn't worth the risk.

 

[Fostereast]

Really silly question but... have you measured the trigger pull? It sounds like you have modified the hammer and trigger springs. If the springs are lighter it's possible the primers used in one type of ammo work and the primers in another type are too hard to fire. As an example, in general any competitive shooter that reloads, tends to reduce the trigger pull and then use Federal primers, because other primers tend not to fire.

It sounds like you have a good handle on the problem, but if the trigger pull is reduced, certain brands of primers become unreliable.

 

[Protocall_Design]

It may be that the recoil is causing the cylinder stop to bounce down during recoil, unlocking the cylinder and allowing it to rotate. If that's the case, a heavier spring may help, or it may still not be strong enough. On some heavy recoil N frames, that was happening as well as the bolt going forward and allowing the cylinder to go sideways. They have since implemented remedies for that, I don't know if the 69 has the same upgrade.

 

[Mike_Fontenot]

Really silly question but... have you measured the trigger pull? It sounds like you have modified the hammer and trigger springs. If the springs are lighter it's possible the primers used in one type of ammo work and the primers in another type are too hard to fire.

The SA trigger pull is about 2-1/2 lbs. But the DA pull is about 9 lbs, and I've never had any light strikes with any ammo.

 

[Mike_Fontenot]

It may be that the recoil is causing the cylinder stop to bounce down during recoil, unlocking the cylinder and allowing it to rotate.

Yeah, that was my diagnosis. I'll know pretty soon if the stiffer spring from Wolff solves the problem.

On some heavy recoil N frames, that was happening as well as the bolt going forward and allowing the cylinder to go sideways. They have since implemented remedies for that, I don't know if the 69 has the same upgrade.

I've never had the problem of the cylinder bolt unlocking, and allowing the cylinder to swing out of the frame.

 

[Mike_Fontenot]

I had some unexpected time today to try to do the spring change in my 69. I initially tried to do it without taking any parts out (other than the spring), but had trouble trying to get the old spring out, even though I wasn't planning on saving it, and was willing to treat it pretty roughly. I didn't have a curved dental pick ... just a couple of pottery tools that my wife loaned me, that were small straight needles mounted in wooded handles, and I had numerous very small screw drivers. I was afraid that even if I was able to get the new spring in (a BIG if), it might well get damaged in the process. So I decided to remove the hammer, rebound slide, and trigger, using several YouTube videos as guidance. I didn't have any problems, but I took it very slow. The hardest part, by far, was replacing the spring in the cylinder stop ... it was much harder for me than for the guys in the videos ... maybe because my spring is stiffer and harder to manage. But I DID finally get it in, and it appeared to work OK. And the reassembly of the other parts went fine. Dry firing seems normal in all respects. I may be able to test fire it with the Underwood 240gr ammo Friday, or perhaps Monday or Tuesday, and see if the problem is gone or not. I SURE hope it's gone.

I was surprised that there were several things about my gun that were different from the older S&W revolvers in the videos I used (they all had the hammers with the attached firing pin). For example, the little safety part that slides in a vertical channel in the frame underneath the rebound slide (I don't remember what it does ... maybe interacts with the cylinder release mechanism somehow(?)) isn't there at all. And the underside of the side plate is quite different ... the narrow long slot that the hammer safety fits into is no longer there.

 

[Protocall_Design]

The safety part that slides in the vertical channel is one of the upgrades to keep the bolt from going forward during recoil. It is operated by an extra long pivot pin on the hand that goes through the trigger and runs in a slot at the base of the bolt block. When the trigger is pulled back, the bolt block rises up, when the trigger is at rest, the bolt block is down so you can open the cylinder. I think they should have done these upgrades on the 69 and 696, but they didn't ask me about it. Nor will they ever.

The sideplate still has a track for the hammer block to run in, but is now made much differently. Originally the slot was made with a slotting (or slitting) saw. Now it's made with an endmill. That eliminates a setup and cutting operation.

 

[Mike_Fontenot]

The safety part that slides in the vertical channel is one of the upgrades to keep the bolt from going forward during recoil.
[...] I think they should have done these upgrades on the 69 and 696, but they didn't ask me about it. [...]

Thanks for that info. I just assumed that, since the Model 69's are less than 4 years old, that they had just found another way to get that feature. Do the new 629's have it?

 

[Mike_Fontenot]

Range trip report:

The "stiffer" cylinder stop spring seemed to have no effect. I got the same failure rate as with the stock spring. Time to send it back to S&W. Bummer.

 

[armorer951]

Have you tried firing the heavier ammo with the OEM (stock) rebound slide spring installed?

 

[Mike_Fontenot]

Have you tried firing the heavier ammo with the OEM (stock) rebound slide spring installed?

I MAY have fired a few Underwoods when I first bought the gun (about four years ago), but it probably was with single rounds being loaded into the cylinder, which wouldn't have exposed the problem. And after I got the trigger job from a local gunsmith (I didn't do the spring change on the 69, I just did it on the 686), I also fired some Underwoods, but again, it was with only single rounds loaded in the cylinder). I think the rebound spring that the gunsmith put on is a little lighter than the 11 lb one that I put on the 686 (even though mine was the lightest that Wolff makes), but the SA trigger pulls are close to the same.

Could the light rebound spring provoke the cylinder stop unlocking during recoil that I'm seeing?

 

[armorer951]

That's a very light rebound spring. The OEM spring is approx 16-17 pounds.

I was concerned about the behavior of the trigger during recoil, and whether it (trigger hook) could somehow interact with the point of the cylinder stop during the heavy recoil phase of firing. It may just be the cylinder stop itself rebounding out of the stop slot in the cylinder. The stop is going to want to go forward when the frame pushes back during heavy recoil.....and if the recoil is severe enough, the cyl stop spring will not be able to prevent this.

Not trying to tell you what to do, but this malfunction is an indication that the loads you are using are beyond the ability of the revolver to accomodate. Continued use of the heavier loadings will certainly shorten the life of the gun, and may even be dangerous for you or for bystanders. You might consider going to a slightly lower pressure load that the frame and contents can tolerate.

 

[Fostereast]

Springs

You might try the original springs prior to sending it back.

 

[BruceM]

Not trying to tell you what to do, but this malfunction is an indication that the loads you are using are beyond the ability of the revolver to accommodate.

^^^^^^^^This^^^^^^^^

I understand this may not be something the OP wants to hear but that doesn't change the facts. The problem he is having mirrors those which provided the impetus for the Endurance Package now standard on the M29's and M629's as mentioned previously. Now he insists on using an even heavier load in a substantially lighter gun.

There may be no easy and inexpensive fix for this problem other than dialing back the ammo a tad.

Bruce

 

[Mike_Fontenot]

I just realized that I don't know why the rebound slide moves aft when the hammer is cocked. Jerry Kuhnhausen, in his S&W revolver shop manual (page 12, item 2 under "Operating Sequence and Safety Features"), says "At the same time, the rebound slide moves to the rear, ...". But he doesn't say WHY it moves to the rear. Anyone know?

 

[armorer951]

The rebound slide moves to the rear because the trigger moves to the rear as it is lifted by the hammer.

If you refer to pages 73, 74 and 75 in the Shop Manual, 5th Edition, you can see how the action moves in SA and in DA. Two different forces at work, one by the hammer (SA), and one by the trigger. (DA)

 

[Hondo44]

More soecifically:

When you removed the trigger to install the cyl bolt spring, remember that rod sticking out of the back for the trigger that nests in a pocket in the front end of the rebound slide. That's what literally pushes the slide back whether trigger movement is initiated by the hammer in SA or by the trigger in DA.

 

[Mike_Fontenot]

More soecifically:

When you removed the trigger to install the cyl bolt spring, remember that rod sticking out of the back for the trigger that nests in a pocket in the front end of the rebound slide. That's what literally pushes the slide back whether trigger movement is initiated by the hammer in SA or by the trigger in DA.

OK ... I understand it now. Where I was going wrong was that I thought the plunger from the trigger pushed on the rear of the rebound spring, but now I realize that it doesn't ... the rear of the rebound spring stays fixed at the rear of the cylindrical channel in the slide. The plunger pushes on the rear of the slide. Makes sense now.

 

[armorer951]

Here are some action drawings that may help as you think about the movement of the action......

AT REST:




DOUBLE ACTION, TRIGGER TO SEAR PICKUP:




DA, TRIGGER, SEAR TO HAMMER EXCHANGE:




DA, HAMMER RELEASE POINT:




SA, COCKED, READY TO FIRE:




SA OR DA, FIRED:

 

[Mike_Fontenot]

Here are some action drawings that may help as you think about the movement of the action......

Thanks. Those are very useful.

 

[skipnsb]

Was the M69 "skipping" problem cured?

What did the factory do/say?

Is the Underwood ammo over SAAMI spec pressure?

Skip

 

[ameridaddy]

Don't take this wrong... but if you can't remove the hammer, which takes a second, I would suggest you get someone with experience to replace the cylinder stop spring... but as others have noted, i doubt that is your problem. You are shooting some very high pressure ammo designed for a N frame in a L frame - better yet, maybe designed for a Much stronger Ruger 44.

I'd have to agree. In the late 70's I shot metal silhouette with a Mod 29, found the max load in the loading tables was my accuracy load, so one weekend a month I'd hammer the gun with 80 rds of very hot 240 gr shells, plus practice.. Every 6-8 months, I'd find the gun doing exactly what you described, wondering how the heck the fired brass got under the hammer when I pulled the trigger. Long story short, a fine gunsmith, the late Fred Schmidt, looked into my problem and would find the gun had to be retimed and the crane straightened. He was of the opinion that the N frame wasn't quite up to the 44 Mag punishment and that the top strap was stretching under max loads. He installed a ball detent for the crane before that was fashionable, and that helped, but I still had to take it back at least once a year for a tuneup until I sold the gun.
IMHO, if you feed your L-frame gun a steady diet of hot 44 Mag loads, you'll continue to have problems. If you want to shoot bear killers, get a Redhawk.
I think your situation is analogous to the Model 19 and max power .357 loads. It won't blow up the gun, but you'll wear it out before its time.

 

[Mike_Fontenot]

[...]
Long story short, a fine gunsmith, the late Fred Schmidt, looked into my problem and would find the gun had to be retimed and the crane straightened.
[...]

Thanks for that info. If those are a problem with my 69, I wish S&W would figure it out and fix it. Do you remember exactly how the timing was "off"?

On the other hand, if nothing's wrong with my gun, I can live with the problem. The full-strength mainspring prevents the actual malfunction, even though there still is cylinder unlocking and a little bit of cylinder rotation.