Seems like a screwy way to do an "action job"

[ric426]

Edit: Ever post something and find that you really didn't know what you were talking about? This is one of those threads, so don't bother reading further if you have anything better to do...

I recently picked up a Model 14-3 that had been converted to a PPC gun. I got to shoot it before buying and it worked well, but after closer inspection I found that the cylinder didn't always carry up to full lock on some chambers before the "DAO" hammer dropped. The gun is plenty accurate, but it continued to bug me that I was seeing a lot of fired cases with off center firing pin strikes and more build up on the right side of the forcing cone, so I dug out my Kuhnhausen manual and started troubleshooting. The cylinder gap and endshake had great specs and alignment seemed right on so I ruled that out. I was going to try an oversized hand, but found that the existing one is already oversized and I wasn't about to try peening ratchets, knowing that that was beyond my skills.

I'd never quite understood what had been done to make the gun DAO, so I sat down at my bench with the side plate off and watched the action closely as I cycled it. It seemed like if the hammer went back a little further in DA before it dropped, the carry up would be fine. The SA notch looked like it hadn't been touched, but the hammer wouldn't pull back far enough to cock in SA because the trigger stop prevented it. On a hunch I removed the trigger stop and lo and behold I had nice SA function. No push off and nice light, crisp trigger action. I had SA back. Cool. That told me that at least the SA hadn't been messed with.

So why was the DA hammer dropping so early? I watched the end of the DA sear and found that it was actually being lifted clear of the trigger nose and that the corner of the trigger below the SA notch was riding the edge of the trigger cam until it dropped off without the DA sear even touching the trigger nose and the hammer dropped. Huh!?!?!. Unless I totally misunderstand how a S&W action functions, that's totally bass-ackwards to be using those two surfaces as a DA sear. It looks like the DA sear was shortened enough to allow that to happen, but for the life of me I don't understand why. No wonder the DA pull seemed inconsistent. Is this a common practice or is this as strange as it seems to me? Do I misunderstand how the action works after all?

I already had a used K frame hammer and trigger on the way because I wanted to try bobbing the hammer (thinking that the gun was DAO) and didn't want to risk the "working" parts I had on my experiment. This morning I ordered a couple of DA sears, a stirrup and misc. pins from Brownell's to make a complete hammer assembly (it already has the hammer nose in place) and I'll follow the Kuhnhausen instructions for fitting a DA sear. I'm not risking any existing parts and it'll be a good learning experience. If I screw up the first sear I've got an extra in case I need to have a gunsmith do it right. If I'm careful and patient (and a little lucky) I'll hopefully end up with a gun that finally functions the way it should. Thanks to all the great info and folks on this forum I feel like I can give it a try without digging myself into a deep whole and making things worse.

 

[500 Magnum Nut]

Sure, someone could have shortened the sear, maybe it was binding? Did you drop cartridges into the chambers to check your timing? Did you check it out with range rods?

The sear is there and needed to assist in cocking the gun in DA. The sear is not needed is SA.
I feel you carry up is not right and needs to be fixed. An oversized hand or new ratchet is the norm. However, your cylinder stop needs to be inspected, as the barrel may not be in alignment with the chambers. I'd check it out with range rods to make sure the CU is right or not. It might show the gun is over indexing so the cylinder stop needs to be checked out also.
While your add it I'll check the yoke alignment too to make sure that is on. If the yoke is twisted, it can look like the CU is off.

On these guns, if one part/area goes out by wear or abuse you need to inspect all areas to properly diagnose which part needs to be adjusted.

 

[tomcatt51]

I watched the end of the DA sear and found that it was actually being lifted clear of the trigger nose and that the corner of the trigger below the SA notch was riding the edge of the trigger cam until it dropped off without the DA sear even touching the trigger nose and the hammer dropped.

That's how it works. Smith's nomenclature is somewhat misleading. The "DA Sear" gets the hammer started back then trigger and hammer surfaces take over until the hammer falls. If you watch the hammer move back (sideplate off and mainspring backed off) as you pull the trigger the DA Sear and trigger are engaged but then the hammer/trigger surfaces engage and the upper trigger surface moves past the DA Sear (not in contact with it) just before the hammer falls. It's alot like gears engaging, engagement passes from tooth to tooth.

 

[ric426]

Clearly, I don't have a proper understanding of how the action works in DA then. Where can I find photos of the lockworks at different points in the DA cycle and the proper nomenclature for the various parts of the trigger and hammer, so I'm at least using the right terms?
I wish I had another S&W revolver to compare so that I don't go spinning off in the wrong directions based on bad assumptions, but at this point I don't. I think part of my confusion comes from this animation
http://www.rattlesnakeridge.org/flash/SW357Mag1.swf
that makes it look like the DA sear controls hammer drop in DA mode.

That's my excuse for today and I'm sticking to it.

 

[ric426]

Sure, someone could have shortened the sear, maybe it was binding? Did you drop cartridges into the chambers to check your timing? Did you check it out with range rods?

The sear is there and needed to assist in cocking the gun in DA. The sear is not needed is SA.
I feel you carry up is not right and needs to be fixed. An oversized hand or new ratchet is the norm. However, your cylinder stop needs to be inspected, as the barrel may not be in alignment with the chambers. I'd check it out with range rods to make sure the CU is right or not. It might show the gun is over indexing so the cylinder stop needs to be checked out also.
While your add it I'll check the yoke alignment too to make sure that is on. If the yoke is twisted, it can look like the CU is off.

On these guns, if one part/area goes out by wear or abuse you need to inspect all areas to properly diagnose which part needs to be adjusted.

I had a local gunsmith check it with a range rod and he said the lockup and alignment was fine. He did a cursory check of the timing and said the gun was safe to shoot, but I got the impression that he wasn't all that interested in revolvers.
Looks like it's time to seek out a good pistolsmith and turn it over to them before I make a mess of things.

 

[tomcatt51]

That video is not a good representation of how DA works. That's causing your mis-understanding. SA is right but not DA. The hammer does not come back as far DA as it does SA. It is also normal for a trigger stop set for minimal overtravel shooting DA will not allow you to cock the gun SA.

 

[ric426]

Well, at least this time I have an excuse for being a dope.

Between, the misleading animation and the previous owner of the gun telling me that it was modified for DAO, I was going off in all sorts of bad directions. If it's true that we learn through our mistakes, I'd expect to be a lot smarter than I am...

I'm still glad I ordered the parts though. That way I can have a complete hammer assembly to experiment with and not risk the functioning parts.

 

[Malamute]

Tuning the transition from the DA sear to hammer sear in DA mode takes a little finesse. That's the part that matters most when doing anything to these parts. It's easy to go too far, then you can have a glitch in the DA stroke. Too little clearance, and it binds (DON'T force it!). When properly fittted, you can't feel the transition. Interestingly, used parts have generally worked quite well when I've tried them in various guns. New parts take fitting.