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The gun:

Completely original 4" SW Model 66 (no dash)
Pinned and recessed with the firing pin on the hammer (I don't know if this is relevant but it gives you an idea for the age of the gun anyway)
No modern keyed safety
low round count - less than 500

A few months ago, about every 30 rounds, the trigger began to lock up (I wasnt able to pull the trigger) so that when I tried to fire the gun, the trigger would stop immediately when I put pressure on it. About half the time that this occured, once I released the pressure from the trigger and then pulled it again, it would fire just fine. When the trigger locks up (not to be confused with putting the gun in full lock mode), I can slightly turn the cylinder with my left hand while maintaining trigger pressure with my right hand, and it will free up. The gun will lock by either pulling the trigger or manually cocking the hammer. This orignally began as a problem with every 30 rounds or so, but now occurs about every 10 rounds. Interestingly, i can't put rotational pressure on the cylinder while pulling the trigger and force the trigger/hammer to lock.

I know this can be easily remedied by a qualified gunsmith, but I'd like to tackle this one myself if I can get an idea for what is causing the problem. Any ideas?

What kind of ammo are you using. Happened to mine with cheap ammo. If it happens after the gun has been fired it could be that the primer is being pushed back causing the cylinder to bind up. Find a m/t shell and put the shell on a table and see if it sits flat. Hope this helps good luck.

Clean it! Take it down as far as you are comfortable with. Soak it, scrub it, get all the gunk out of the nooks and crannies you can find. Lube and try it again. Naphtha or kerosene are good cleaners to soak the parts in.

I had about the same problem on a Mod. 29 (44mag) the screw holding the main spring had come loose. It would lock up when it got hot after about ten rounds of magnum.

Thanks for the replies. Based on your advice, this is what I found:
- cylinder gap is .004". Nice and tight, but not binding
- springs were set in place with no problems
- I tore it completely down last night and cleaned it wtih gun scrubber. It was clean to begin with, but now even better. I'll head to the range later this week to see if that did the trick.

I found something else as I was messing with it. I can force the malfunction by putting counter-clockwise pressure on the cylinder while I'm trying to pull the trigger. It seems like the part that extrudes from the bottom of the frame up into the cylinder to keep the cylinder in the firing position (I don't know what it's called) is not moving down when the trigger is pulled and is binding on the cylinder. If the cleaning didn't fix it, I'll take it back down again and look for worn or bent parts.

I'll let you know how it goes.

Tregs wrote: It seems like the part that extrudes from the bottom of the frame up into the cylinder to keep the cylinder in the firing position (I don't know what it's called) is not moving down when the trigger is pulled and is binding on the cylinder.

Probably a broken or very gunked up cylinder stop spring. If you don't want to take it to a gunsmith and like to work on your guns, I would suggest getting a copy of Kuhnhausen's book, "The S&W Revolver". The cost of the book and the replacement spring would be less than a gunsmith. Try http://www.brownells.com" onclick="window.open(this.href);return false;

If you don't like working on guns, take it to a smith. The problem is internal and exterior cleaning will not do anything.

Gringop

Thanks for the advice on tearing down the gun and completely cleaning it. It didn't look dirty, but I tore it completly down and soaked it in gun scrubber, oiled it up, put it back together, and took it to the Garland range today. 40 flawless rounds, except for one ammo issue.
I noticed that I typo'd my original post. The gun has about 500 rounds through it, not 2500.

Thanks for the advice. It worked.