inspecting s&w model 10 mainspring

DTHughes · 01-10-2012, 11:54 AM

Short history: You've seen this in other threads. I got it at a gun show as a fixer-upper. Pistol was a Phillipines police trade in, Model 19-5, much (MUCH) work done by some previous owner. Ball detente on the crane, top strap tapped for a scope, etc. Dealer I got it from replaced the bobbed hammer with a target hammer. There's a set-screw in the bottom of the grip that will allow partial extraction of the strain screw allowing reduced DA pull. Or there was, that's now an expoxy filled hole. I've got all the issues it had with end-shake and timing worked out and took it to the range to very carefully test-fire it for a bit. Shooting a light load behind a 158gr SWC on Winchester brass with Federal small pistol primers. SA pull was nice, accuracy was exactly what I would expect from even an abused 19: good.
OK. Double-action drills. The routine became bang bang click. About 3 per second double-action (I'm not Elmer Keith). Following "click" looked to make sure and the cartridge had not fired, barely a dimple on the primer. Those that did fire had a good solid hit on them.
Back home and tore it all down. No binding or problems with the lockwork. I've ordered a new mainspring and tension screw from Numrich. Anyone have other suggestions of likely culprits for very light strikes in DA?
Thanks.
Dave

JohnnyT · 01-10-2012, 01:47 PM

Quote:

There's a set-screw in the bottom of the grip that will allow partial extraction of the strain screw allowing reduced DA pull. Or there was, that's now an expoxy filled hole.

Whoa!

The "set screw" is not a DA trigger pull adjuster. It's supposed to be screwed all the way in.

First things first...

If the screw is missing...what keeps tension on the mainspring?

DTHughes · 01-10-2012, 02:05 PM

Quote:

Originally Posted by JohnnyT

Whoa!

The "set screw" is not a DA trigger pull adjuster. It's supposed to be screwed all the way in.

First things first...

If the screw is missing...what keeps tension on the mainspring?

Woops. Sorry JohnnyT. Let me clarify: The strain screw is present and it is screwed all the way in. Someone had added a set screw 90 deg to the strain screw so that you could back the strain screw out a turn or two and then lock it in place to adjust DA trigger pull. I'm aware that is NOT a good idea, so, I took out the set screw (was on the bottom face of the grip frame) and tighetened the strain screw (where 3rd finger would normally live in shooting position) all the way down. I bought new parts for those guessing that the person who tried to lighten the DA pull may have tried to re-form the mainpring or file just a teeny bit off the strain screw.
Clearer(ererer)?

A picture is worth at least 5 words:

Dave

dfariswheel · 01-10-2012, 05:40 PM

Other possible reasons for light strikes in a S&W:

Excess end shake of the cylinder.

Improper head space.

Fouled chambers.

Short, bent, wrong, or worn firing pin.

As above, altered or weak mainspring---Shortened strain screw.

Hammer/trigger altered, worn, or broken causing short hammer fall in DA.

Bent/broken, corroded/fouled hammer pin causing mushy hammer fall.

Interference with the hammer causing mushy hammer fall.

JohnnyT · 01-11-2012, 03:18 AM

I think that pretty well covers it.

Look at the breechface while you're at it and check for deformation around the firing pin/hammer nose hole. I've run into that a couple times.

DTHughes · 01-11-2012, 06:22 AM

Thank you, gentlemen. You've given me some more food for thought and places to explore.
Dave

exfed2002 · 01-13-2012, 05:59 AM

Quote:

Originally Posted by DTHughes

Someone had added a set screw 90 deg to the strain screw so that you could back the strain screw out a turn or two and then lock it in place to adjust DA trigger pull.

Power Custom sells such a setup, along with aftermarket sideplate screws, trigger stops, etc.

Welcome to Power Custom

01-10-2012, 11:54 AM	#1
DTHughes Member Join Date: Jan 2011 Location: Newton, KS Posts: 64	Light DA Firing Pin Hits on S&W 19-5 Short history: You've seen this in other threads. I got it at a gun show as a fixer-upper. Pistol was a Phillipines police trade in, Model 19-5, much (MUCH) work done by some previous owner. Ball detente on the crane, top strap tapped for a scope, etc. Dealer I got it from replaced the bobbed hammer with a target hammer. There's a set-screw in the bottom of the grip that will allow partial extraction of the strain screw allowing reduced DA pull. Or there was, that's now an expoxy filled hole. I've got all the issues it had with end-shake and timing worked out and took it to the range to very carefully test-fire it for a bit. Shooting a light load behind a 158gr SWC on Winchester brass with Federal small pistol primers. SA pull was nice, accuracy was exactly what I would expect from even an abused 19: good. OK. Double-action drills. The routine became bang bang click. About 3 per second double-action (I'm not Elmer Keith). Following "click" looked to make sure and the cartridge had not fired, barely a dimple on the primer. Those that did fire had a good solid hit on them. Back home and tore it all down. No binding or problems with the lockwork. I've ordered a new mainspring and tension screw from Numrich. Anyone have other suggestions of likely culprits for very light strikes in DA? Thanks. Dave

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01-10-2012, 05:40 PM	#4
dfariswheel Senior Member Join Date: Jun 2001 Posts: 1,800	Other possible reasons for light strikes in a S&W: Excess end shake of the cylinder. Improper head space. Fouled chambers. Short, bent, wrong, or worn firing pin. As above, altered or weak mainspring---Shortened strain screw. Hammer/trigger altered, worn, or broken causing short hammer fall in DA. Bent/broken, corroded/fouled hammer pin causing mushy hammer fall. Interference with the hammer causing mushy hammer fall.

01-11-2012, 03:18 AM	#5
JohnnyT Senior Member Join Date: Apr 2010 Location: North Carolina Posts: 724	I think that pretty well covers it. Look at the breechface while you're at it and check for deformation around the firing pin/hammer nose hole. I've run into that a couple times.

01-11-2012, 06:22 AM	#6
DTHughes Member Join Date: Jan 2011 Location: Newton, KS Posts: 64	Thank you, gentlemen. You've given me some more food for thought and places to explore. Dave