Had a peculiar thing happen the other day at the range. Shooting my M66-2 with some light target WC ammo. Double action shot well. Single action had a problem...

When squeezing the trigger to the break point, the hammer fell half way and stopped. If I continued the trigger pull the hammer fell from the half-way point without enough force to ignite the primer. Back home, I tried to repeat the behavior with the gun unloaded. For the most part the hammer fell as expected. But once in a while it would fall half-way and stop. It even happen once dry firing double action. That time I confirmed that the hammer was being held back by something in the trigger linkage.

Anyone have any ideas on what might be happening and what should be done to fix it? I could ship it off to S&W to get it fixed, but an occasional problem is typically hard to diagnose...

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Gun Control: POA=POI

First I would give it a good thorough cleaning. It may just be some gunk that got inside and is occassionaly causing problems. You may even have to remove the sideplate to get inside. Don't take it apart any further unless you really know how they are put together, just spray some cleaner in it and let it work the gunk out.

Make sure the gun is empty. Try taking the grips off and cycle the action paying close attention to what your main spring is doing and how it is effecting the hammer.
The main spring screw that is in front of the grip frame may have been loosened too much which could be why your primers are not igniting.

Some people loosen this screw to lighten the action slightly but too much loosening of the screw can cause the mainspring not to function properly.

I am by no means an expert, but you might want to pick up a S&W shop manual for revolvers. Can be purchased at Brownells. It will give you a much better insight into how the internal parts work.
When in doubt, don't touch it. Send it to S&W or see if you have a reliable gunsmith in your area.

That happened to a friend of mine a few years ago, with a Colt .22 revolver. removal of the side plate, a little cleaning and a drop of oil and it was fine again.

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H Richard
SWCA1967 SWHF244

Thanks, everyone. I have the S&W Revolver Shop Manual and a good cleaning sounds like a good first step. I'll let you know what I find.

Dan

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Gun Control: POA=POI

I thought this might be useful to others, so here is an update on my M66 problem.

I did a detailed disassembly of my M66. Once I got the side plate off, I was surprised that it wasn't filled up with old oil and powder residue. There was some gunk visible at first glance, but just not enough to jump out at me yelling "It was my fault!"

However, after doing a thorough cleaning of all of the parts, I began examining the mechanisn to see how it worked. What I discovered is this:

1. the works were dragging in enough oil sludge at pivot points that some small motion was retarded (i.e. increased friction = reduced momentum = lost potential mechanical energy).

2. As I cycled the hammer/trigger, I carefully watched the points of contact until I had a good sense of what was happening. (It really is an elegant bit of engineering design!)

3. Then I saw it! The single action sear was slightly rounded on the trailing edge, allowing the hammer to release just a bit early. If I was squeezing the trigger slowly, the back edge of the trigger did not rotate sufficiently and the sear caught on a clearance depression on the heel of the trigger, just below the hand pivot point. It was just enough to stop the hammer fall. If I squeezed the trigger just a little bit faster, the sear cleared the depression and continued to fall. But, in some cases, the sear dragged against the heel edge of the trigger and slowed down the trigger fall. In that case the firing pin wouldn't hit the primer hard enough to fire it.

4. After cleaning and lubricating everything, I put it all back together and tested the single action mechanism again. The action was just noticably smoother. And I had a hard time getting the hammer to hang in mid fall.

5. Conclusions:
a. The gun was overdue for a detailed cleaning
b. The single action sear needs to be looked at by a gunsmith
c. A new hammer might be needed if the sear can't be cleaned up
d. There doesn't appear to have been an action job performed on this gun
e. Single action reliability is still in doubt, double action is fine.

I also noticed when I had everything disassembled that there is some evidence of pitting on the side of the cylinder at the edge of the foreward face. It looked like a line of burned powder deposited there, but after getting it clean, I found the pitting under the dirt. The cylinder face is also pretty blackened and very hard to clean where it comes against the forcing cone. Possible flame cutting?? There is also just a touch of flame cutting marks on the underside of the top strap, just above the forcing cone. Possibly an end play problem?

So I guess my M66 is going to need a bit of TLC from a good gunsmith. I'll probably call S&W and talk with them about it first...

Dan

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Gun Control: POA=POI