[capstan]

I have a python that fires perfectly in single action but when using double action it often doesn't fire. When this happens I can see that the primer mark is off center. While doing some simple timing tests I noticed: I use my finger to prevent the cylinder from free wheeling and pull the trigger very slowly, the hammer drops before the cylinder has advanced enough to lock. This sounds like a problem to me but I'm no expert. Any thoughts are welcome. Thanks.[/QUOT

When doing your slow cock test, the cylinder "bolt" (smith and Wesson calls it cylinder stop),should drop in about the middle third of the groove leading into the cylinder notch. When the cocking is complete (hammer is all the way back),the bolt should be IN the notch. If it is not in the actual notch when hammer is all the way back ,it is technically out of time. BUT, when squeezing the trigger, the second stage/finger of the hand will push on the cylinder rachet tooth to turn the cylinder a little more,so that the bolt drops into the notch, right before the gun goes off. I have had several Colt revolvers of this older action type that have exhibited this issue. Unlike a Smith and Wesson action,They ALL locked up when trigger was pulled, however. Now there may be a case where that doesn't occur due to maybe Extreme wear, but I just haven't come across that yet.
The typical solution for the bolt dropping too early and not locking up when hammer is back -is to stretch the hand so it pushes the cylinder around more, so the bolt always drops into the notch when hammer is all the way back, even though it is usually not necessary (to effect a final lock up), because of the second stage hand movement during trigger pull.

Another issue is when the bolt drops into the groove/lead too LATE-i.e. it is not in the middle third of the groove but closer to the notch -maybe dropping right near the edge of the notch and when hammer is back with your slow cock test, the bolt IS in the notch. BUT this is STILL out of time -but the other way -bolt drops Too far BEYOND the middle third of the groove. This is the more disturbing situation -in that when pulling the trigger in double action, the momentum of the cylinder will often cause the bolt to hit just beyond (or way beyond)/on the other side of the notch. I this case it won't be in the notch when the hammer hits.
I had a couple Det Spls. that did this. In one case ,pulling the trigger in double action failed to fire the gun,and the bolt was way beyond the notch and no primer dent .Depending upon how fast or slow you pull the trigger ,the cylinder momentum could cause bolt to maybe drop just a tiny bit beyond, but just enough to still hit the edge of the primer. That could be a real problem if round went off with chamber too far off alignment with bore.

From your description ,it sounds like the late bolt drop may be the problem rather than an early bolt drop.But then that's just my guess -Could be something altogether different also, I suppose.
Please let us know what the Gunsmith's final diagnosis is.

 

[capstan]

Excellent. THANKS! for letting us know what He found to be the actual issue. I would think that is a relatively uncommon issue-

I know that sometime in the 80's there was a big union strike and quality supposedly took a dive. But I thought that was more like mid 80's. Anyway,this is more good info. for future reference.