S&W M19 trigger pull gets heavier under use

[Jenrick]

I'm putting this here rather then the gunsmithing section as I'm curious if anyone's encountered this before, versus how to fix it.

So a friend asked that I do a little light work on his M19. Nothing crazy, polish the trigger rebound slide, change the rebound slide spring for a lighter one, clean the internals while I was there. Nothing involving tools, files, etc.

Prior to popping open the side plate I ran about a box of 50 standard pressure Speer Lawma .38 Sp rounds through just to see how it shoot. Stock trigger bascially, but by the time I got the end of the box it had a noticeable heavier trigger pull. I figured it was simply a lack of cleaning and lube on the crane, as he said he hand't messed with it in years.

So I pop of the crane and cylinder, remove the side plate and did the requested work. No biggie, nothing too dirty, just some cleaning and some lube here and there. I reassemble the pistol, and the trigger is noticeably smoother and a touch lighter. Just what I was expecting.

I ran two boxes of the same ammo (standard pressure .38 spl) through at a moderate pace, about 30 mins to fire 100 rounds total. This time the trigger started to get heavier around the 60th round. I stopped to see if anything was binding, had come loose, etc. I checked the screws, etc, and found nothing. I fired another 6, and the trigger was back to being what I expected. After about 18 more rounds it started to stiffen back up.

The first thing that comes to mind is the gun is heating up and binding ever so slightly. I didn't have any gauges with me to check cylinder gap, cylinder to frame clearance, etc. So at the moment all I've got is a hunch. Has anyone run into this before?

-Jenrick

 

[mjones 59]

I have put 50-100 rounds through mine weekly
for the last four months without any issues.
If you let it cool down does it get smoother?
When you clean under the star extractor is
there a lot of build-up?

Sorry not much help.

 

[Jenrick]

It's appears to smooth up when it's cold. I'll verify that fact tomorrow.

Nothing under the extractor worth mentioning.

-Jenrick

 

[Driftwood Johnson]

Howdy

Just a hunch. You might want to check if the extractor rod is slightly bent. If so, perhaps the cylinder is rotating slightly tilted (for want of a better word) and perhaps as the gun heats up the cylinder starts rubbing on the end of the barrel.

Perhaps.

Did you notice whether it was happening on just a few chambers or not?

Just a thought.

 

[Iggy]

Maybe your trigger finger is getting tired..

 

[Taurus 617 CCW]

I would also check cylinder rotation to make sure that it is not binding. On lesser expensive revolvers I have seen the cylinder bind because of carbon build up, etc. Just a thought.

 

[9mmepiphany]

Have you checked the cylinder for excessive end shake?
The problem is that sometimes when you fix the end shake, you'll need to have the cylinder gap adjusted

It might be that the cylinder just needs to be fitted.

 

[Jim K]

It sounds like a too-tight barrel-cylinder gap. The cylinder lengthens as it heats up and binds. Some folks think a tiny b-c gap is good, but if it runs .002" or under you can get what you are experiencing. It should run .006-.007".

People often blame the binding on dirt or buildup of burned powder; cleaning relieves the problem, not because the gun was dirty, but because stopping firing for cleaning allows the gun to cool off.

Jim

 

[eldon519]

I used to have one piece of brass out of one lot I reloaded that had a thicker than normal rim that dragged. Maybe try a different brand of ammo. Could be a combination of heating and something like that.

 

[gotboostvr]

I'm thinking BC gap as well. It might not be the only issue though.

My 686 would do the same thing after a few hundred rounds. It was a combination of heating up with a tight BC gap and a little fouling on the cylinder face, as long as I kept one or the other in check it was okay.

 

[Drail]

Yup, you gotta have sufficient gap and you got keep the buildup down on a tight revolver.

 

[BCRider]

Another heat related item might be that if the lockup is a hair tight that the warming is altering the dimensions enough that the hand is pushing the cylinder against the stop bolt with some force just before the trigger drops. If it's this you'll feel a nice normal trigger until just before the hammer break when in double action and a slight bind right at the end of the hammer cocking stroke.

If it's the BC gap closing and rubbing you'll see signs of the rubbing on the cylinder's front face and feel the rubbing through the whole trigger stroke when shooting in double action or through your thumb if cocking the hammer for an SA shot.

 

[spazzymcgee]

Cylinder gap would be the most probable issue, and it's easy enough to check. So check that first and report back.

 

[BSA1]

A set of automotive feeler gauges will let you check the b/c gap. When checking the gap measure the gap from both sides of the barrel.

 

[Jim K]

My printer paper is just about .0025". If the cylinder won't close on a piece of printer paper, the B/C gap is too small. If it closes or just closes on doubled paper (.005-.006") then it should be OK.

Jim

 

[Jenrick]

It's definitely a too small BC gap, it wont close of a piece of printer paper.

-Jenrick

 

[pbearperry]

Check for powder residue under the star of the ejector.If it does not seat flush, trigger pull will get heavier.

 

[Jim K]

I think you found the problem. Make sure there is nothing else, like pbearperry suggests. If that is OK, have your friend give S&W a call and see what they say. It might be within their specs, but if not they might fix it under warranty. Even if not, they will do the best job and probably the quickest.

He can take it to a local gunsmith, but make sure the GS has the tools to do the job right and can give him a reasonable repair time.

Jim

 

[Iron Sight]

After a few or several rounds fired the chambers may be somewhat fouled/ dirty and not allowing loaded cartridges to insert fully causing resistance to the cylinder rotating.

 

[Zaydok Allen]

After a few or several rounds fired the chambers may be somewhat fouled/ dirty and not allowing loaded cartridges to insert fully causing resistance to the cylinder rotating.

This seems unlikely, but possible.

If fouling and crud rings are to the point that they are hindering loading, I'd be more concerned about excessive pressure when shooting magnums than anything, as you'd be pushing that crud to the edge of the case mouth or pushing cartridges past the 38 special crud ring, so there is fouling between the chamber walls and the brass. I would think this would only be possible if shooting 38 specials first, and then switching to 357 magnums. Sticky extraction as well as loading would be a good indicator. Also, the blast shield would be pretty scuffed up and the bluing would show signs of wear.

I suppose if the cartridges are so completely undercharged that the brass is not expanding completely before the bullets leave their cases this could happen, allowing fouling to back flow around the brass. Fouling and the tell tale scorch mark on spent cases would indicate this.

The op hasn't mentioned sticky loading or extraction so the tight BC gap seems more likely.