Light Hammer Strikes

[Twist]

I have a M14-3 PPC gun that seems to have an intermittent misfire problem. Every hundred or so rounds it provides a light hammer strike, leaving a tiny indent right in the centre of the primer.
I have shot the gun in competition for the past 10 years and it has suffered this problem off an on for the whole time. I have replaced the hammer nose, rivet, mainspring, checked that the hammer was not hitting the rebound slide, removed (and replaced) the hammer block, clearanced the cylinder release, shimmed the hammer and trigger, set endfloat at absolute minimum, fitted a new hand (so the gun locks up way before hammer fall), checked the headspace (spot on 66 thou)and use only Federal 100 SPP's.

There are no obvious signs of anything impeding the hammerfall. I am confounded with the matter.

Any suggestions with what to look at next ?

 

[Twist]

I have a M14-3 PPC gun that seems to have an intermittent misfire problem. Every hundred or so rounds it provides a light hammer strike, leaving a tiny indent right in the centre of the primer.
I have shot the gun in competition for the past 10 years and it has suffered this problem off an on for the whole time. I have replaced the hammer nose, rivet, mainspring, checked that the hammer was not hitting the rebound slide, removed (and replaced) the hammer block, clearanced the cylinder release, shimmed the hammer and trigger, set endfloat at absolute minimum, fitted a new hand (so the gun locks up way before hammer fall), checked the headspace (spot on 66 thou)and use only Federal 100 SPP's.

There are no obvious signs of anything impeding the hammerfall. I am confounded with the matter.

Any suggestions with what to look at next ?

 

[judge]

Since all the usual parts have been replaced, is the strain screw fully seated - is the strain screw at full length, a new strain screw is aprox. .613 length (overall) for square butt guns. If the strain screw is full length and seated, and the mainspring is new, my guess is that the primers are not fully seated. How does it shoot with factory .38 ammo??

 

[tomcatt51]

What's the weight of your DA pull? If the sear has too much angle, sits too far forward, it can catch the trigger moving by and cause misfires.

 

[bountyhunter]

My guess would also be the strain screw. There are a lot of gunsmiths who grind the ends off them to reduce DA trigger pull.

If you install a new full power (stock) mainspring and a new strain screw, your DA pull should be in the 10 - 12# neighborhood and you should not have misfires.

 

[Joni_Lynn]

If you want to increase the mainspring tension just a bit to see if it fixes the problem, place a used empty primer cup over the tip of the mainspring tension screw and retighten. It will add a bit more pressure and may give you an answer as to what the problem is or isn't.

 

[bountyhunter]

Originally posted by Joni_Lynn:
If you want to increase the mainspring tension just a bit to see if it fixes the problem, place a used empty primer cup over the tip of the mainspring tension screw and retighten. It will add a bit more pressure and may give you an answer as to what the problem is or isn't.

Good idea, that is a common "cure" for a shaved strain screw. Problem is, the little suckers fall out when you clean the gun.

You can also bend the mainspring a touch (make it more flat) and get a bit more strike energy to make up for the shorter screw.

 

[Twist]

The gun is a custom built for PPC competition, it has a Wolff ribbed mainspring, cut 11lb Wolff rebound spring and a standard length strainscrew (fitted with the Power Custom locking screw).
Double action pull is around 6lbs with 32oz of hammer tension (measured at full rearward stroke).
The primers are all seated 3 thou below flush and are loaded on Dillon equipment.
The hammer strikes are all central on the primer, even the light ones. I am feeling like it could be the hammer sear hitting the trigger.

Do you mean the actual engagement ledge on the hammer ? or the double action fly that engages on the trigger cam ???

I wanna get to the bottom of this thing and am willing to get the Dremel out to fix it !!!

 

[john traveler]

Let's not get rash with the Dremel tool...

I have seen more guns messed up with Dremel tools than all other reasons combined.

You can check for yourself to see if the trigger SA sear and the hammer SA sear are interfering. trigger cock the action through a DA cycle, and hold the hammer back using the thumb of your other hand to ease it down. If the bottom of the SA hammer sear is catching on the trigger nose you can feel it. Cycle repeatedly, and look for any roughness or catching in the hammer travel. Next look and feel for full hammer travel as the nose (firing pin) strikes the frame and enters the recoil shield hole. Notice any roughness or catching during hammer fall? Lastly, remove the sideplate and repeat these cyling actions, and pay particular attention to how everything engages and interacts. A light primer strike is usually caused by light mainspring tension, shortened strain screw, marginal FP protrusion, excessive cylinder endplay, or, rarely, hammer/trigger interference during cycling.

 

[bountyhunter]

Originally posted by Twist:
The gun is a custom built for PPC competition, it has a Wolff ribbed mainspring,

I would REALLY put in a new strain screw before grinding anything. The curved sides of the rib are notorious for "coning" the head of the strain screw as the screw turns in and out. That reduces the effective length and you get misfires.

I have seen this many times and I quit using the wolff springs on my guns because of it.

AND POINTING OUT THE OBVIOUS:

The wolff reduced power mainsprings are about 30% less striking force than stock..... which means occasional misfires will happen especially if the ammo primers are not well controlled. That's the reason the wolff site has those disclaimers everywhere about not using RP springs in duty weapons.

 

[Twist]

Bountyhunter,
There is still plenty of adjustment left on the strain screw - about a half turn.... but the problem is more intermittent than consistent... I have tried springs other than the Wolff... the problem is still there and the trigger pull is not as progressive.. those Wolff springs make a tuned action feel real nice!
After about a 150,000 rounds of 38 reloading in the last 10 years I think that the Dillon 1050 just about has the primer seating worked out ! This problem is mechanical and in the gun... I am determined to resolve it.

 

[tomcatt51]

Originally posted by Twist:
Bountyhunter,
There is still plenty of adjustment left on the strain screw - about a half turn.... but the problem is more intermittent than consistent... I have tried springs other than the Wolff... the problem is still there and the trigger pull is not as progressive.. those Wolff springs make a tuned action feel real nice!
After about a 150,000 rounds of 38 reloading in the last 10 years I think that the Dillon 1050 just about has the primer seating worked out ! This problem is mechanical and in the gun... I am determined to resolve it.

The hammer's "bobbed"? The trigger pull weight with the rebound spring you're running should go bang consistently. I assume you have a pinned sear. Kuhnhausens book goes into the sear angle. Sear, the spring loaded piece. You replace it, or peen the top end slightly to pull it "back" slightly. There's a good chance that occaisionally you're getting off the trigger quick enough for the sear to "catch" on the trigger instead of passing by. On MIM non-pinned sears you put a little bevel on the bottom front corner. You see many with a little bevel cut during assy.

 

[bountyhunter]

Originally posted by Twist:
Bountyhunter,
There is still plenty of adjustment left on the strain screw - about a half turn.... .

Are you saying you shoot the gun with the screw 1/2T away from being tight? With a wolff spring, that screw should be dead tight.

Originally posted by Twist:
problem is more intermittent than consistent... I have tried springs other than the Wolff... the problem is still there and the trigger pull is not as progressive.. those Wolff springs make a tuned action feel real nice!
After about a 150,000 rounds of 38 reloading in the last 10 years I think that the Dillon 1050 just about has the primer seating worked out ! This problem is mechanical and in the gun... I am determined to resolve it.

If there is an interference point, I believe you should be able to see it with the side plate off if you slow cycle the action.

As a reference: have you measured the DA pull?

OK, let us know what you find.

 

[Twist]

Update: I have replaced the firing pin bush with a new one. The old one had an elongated hole (probably caused by millions of dry fires without snap caps.)

The hammer nose seems to have a fair bit of side to side play... I am going to get a new hammer nose and rivet from Brownells and may just tighten up the hammer nose groove a tiny bit to reduce the wobble... and then see what the result is.

Stay tuned.

 

[Twist]

Update: Replaced the hammer nose and rivet.... and tightened the hammer nose in the hammer itself. There is still enough movement to allow it to self align with the hammer nose bush. I have also re-shimmed the hammer to get it falling dead square to the bushing.
So far 300 rounds and nary a bobbble.