Percussion lock help?:

[Wingshot]

What cause the cock to be pushed forward at full cock even with the lock out of the gun? I had some issues yesterday with the gun firing after pulling the hammer back to full cock without touching the triggers. I took the triggers out, tuned them a bit, opened the sear mortise a bit because it looked like there was contact with the wood. I was testing the lock in my hand and I can push it off full cock without touching the sear bar. Suggestions?

[rich pierce]

The sear/tumbler engagement is off. Possible reasons:

1) the sear nose is cracked off, rounded off, or has a bad angle where it engages the full cock notch.
2) the full cock notch is messed up or the angle is not a radius to the tumbler axle.
3) both
4) (contributing factor) the sear spring puts no pressure on the sear arm.

[Wingshot]

The sear/tumbler engagement is off. Possible reasons:

1) the sear nose is cracked off, rounded off, or has a bad angle where it engages the full cock notch.
2) the full cock notch is messed up or the angle is not a radius to the tumbler axle.
3) both
4) (contributing factor) the sear spring puts no pressure on the sear arm.

So I’ll need to tear it down and examine it for those possibilities? Any safe alternatives you can suggest since I don’t have a mainspring vise handy?

[Longknife]

4) (contributing factor) the sear spring puts no pressure on the sear arm

I would, check #4 first, maybe loosen the screw that the sear pivots on, it could be binding. You should be able to see if sear nose is, broken or worn and if notch in tumbler is worn without dis assembly....Ed

[SHARPS4953]

After checking the sear and sear spring I would also check that there's no wood swell interfering with any of the lock internals. I compete in the N SSA and find wood swells every few years especially if you get it wet. Just a matter of trimming. But on a 2nd note if your hammer is moving forward on half cock you probably need the new sear. 
Scott

[Bob Roller]

After checking the sear and sear spring I would also check that there's no wood swell interfering with any of the lock internals. I compete in the N SSA and find wood swells every few years especially if you get it wet. Just a matter of trimming. But on a 2nd note if your hammer is moving forward on half cock you probably need the new sear. 
Scott

Who made it? If the maker is still active maybe parts are available.
Bob Roller

[Wingshot]

After checking the sear and sear spring I would also check that there's no wood swell interfering with any of the lock internals. I compete in the N SSA and find wood swells every few years especially if you get it wet. Just a matter of trimming. But on a 2nd note if your hammer is moving forward on half cock you probably need the new sear. 
Scott

Who made it? If the maker is still active maybe parts are available.
Bob Roller

Bob, it’s an older DGW Tennessee Mountain Rifle in .32. Got it off a friend who got it from an estate. It doesn’t move off half cock, only when at full. It appears that everything is still engaging properly, then again I’m no lock expert.

[Wingshot]

After checking the sear and sear spring I would also check that there's no wood swell interfering with any of the lock internals. I compete in the N SSA and find wood swells every few years especially if you get it wet. Just a matter of trimming. But on a 2nd note if your hammer is moving forward on half cock you probably need the new sear. 
Scott

My first thought was clearance and I opened that mortise up a bit to be sure. That’s when I started operating the lock OFF the gun and observed I could push it off full cock.

[rich pierce]

I know folks (certainly not referring to myself) who use vise grips on mainsprings and live to tell about it.

Everyone should own a mainspring vise.

[D. Taylor Sapergia]

If you don't have or want (?) a mainspring vise, cut a rectangular notch in a piece of 1/8" steel sheet that will just slip over the spring when it is at half cock.  Then relax the tension of the spring by taking the lock out of half cock. The 'vise' you've made will hold the spring in that attitude so you can slip the whole thing out of the lock.  But be careful, and get it back into the lock as soon as you can.
Buy a mainspring vise.  I have four.

[Wingshot]

I know folks (certainly not referring to myself) who use vise grips on mainsprings and live to tell about it.

Everyone should own a mainspring vise.

Added to cart. Planned on getting one before I needed it but I guess that didn’t work out.

[mikeyfirelock]

In a pinch ( or sometimes not) I’ve used an adjustable wrench ( crescent wrench ) as a mainspring vise. Put the lock in full cock, adjust the wrench jaws to SLIDE over the mainspring ,leaving a little play, and then let the cock come forward while depressing the sear.   Leave the spring in the adjustable wrench till ready to reassemble lock, then perform same in reverse.  If you’ve left some little play in as directed, when you reassemble, there will be a little “slack” in the mainspring /tumbler and pulling the cock back will release the grip of the wrench on the mainspring.  Easier done than explained.  Mainspring vise is MUCH to be preferred, but this will work in a pinch............................... ( or  oftener if you live in Indiana)
Mikeyfirelock ( proud Hoosier )

[Wingshot]

Thanks all, I’ll wait for vise to get here, not in a hurry to screw this up. I’ll probably post up again once I get it broke down.

[RichG]

If it's an old Dixie lock I would think they would have replacement parts if necessary.

[Scota4570]

A close up picture of the sear nose and full cock notches would be helpful.  The sear nose is probably rounded off.  This could be wear, soft steel, the dremil fool, or unforeseen trouble.  The full cock notch could be rounded or broken.  A shotgun approach would be to replace both if you can get them.  The sear return spring tension should not matter if the angles on the sear nose and tumbler are correct. 

[Wingshot]

A close up picture of the sear nose and full cock notches would be helpful.  The sear nose is probably rounded off.  This could be wear, soft steel, the dremil fool, or unforeseen trouble.  The full cock notch could be rounded or broken.  A shotgun approach would be to replace both if you can get them.  The sear return spring tension should not matter if the angles on the sear nose and tumbler are correct.

Half and full cock:

[rich pierce]

Those notches and sear nose are not well finished.

[Wingshot]

Those notches and sear nose are not well finished.

I thought the same thing Rich. Is it worth some file work?

[rich pierce]

Ideally both are too hard to file. If they are not, they will wear quickly.

You’ve already got an unsafe lock but still, it could be made unrepairable without replacement parts if you’re not very skilled and knowledgeable and have the right tools. Given you’re asking the questions and don’t have a mainspring vise I’m guessing this would be your first try to tune a lock.

Removal of more than a few thousandths changes cock travel and sear arm position. Any changes have to be very careful and slight.

[Wingshot]

Ideally both are too hard to file. If they are not, they will wear quickly.

You’ve already got an unsafe lock but still, it could be made unrepairable without replacement parts if you’re not very skilled and knowledgeable and have the right tools. Given you’re asking the questions and don’t have a mainspring vise I’m guessing this would be your first try to tune a lock.

Removal of more than a few thousandths changes cock travel and sear arm position. Any changes have to be very careful and slight.

You are correct on all counts. I checked a 4 year old DGW catalog and they list everything but the sear itself as available. I’ll call them and see what and if they still have any parts available. I do have some gun builders nearby to consult with and this scenario may just accelerate my going ahead and purchasing an L&R lock and converting to flint. I appreciate all the help.

[rich pierce]

Good thinking. This one is surely salvageable as far as staying on full cock but it could work fine or have other issues once the current problem is fixed. It may be a gamble to swap out the parts. They may not be much better. It looks like the unfinished cast parts were hardened then assembled.

Those closeups were great; easy to see what’s going on.

[L. Akers]

It looks to me like the nose of the sear has close to the correct angle, the tumbler does not.  Careful stoning of the tumbler notch to bring the face of the notch parallel to that of the sear nose would probably solve your problem.  If the geometry is correct, pushing on the back of the hammer should not cause the sear to slip from the notch--even with no sear spring.  The sear spring is responsible only for insuring the sear positively engages the notch.  The lock geometry holds it there. 

[Daryl]

Appears that way to me as well. Too, the sear's nose appears to be rounded in the picture.

[greybeard]

Not that hard to make with a hack saw and good files and patience!!

[Wingshot]

 Thanks to all for the help and encouragement, you all are the best. FYI the photos were taken with my IPhone 11. A great camera and magnifying glass when you need it. I’m going to make arrangements to take the lock down to my friends shop, he’s forgotten more about such things then I’ll ever hope to know. I’m confident now that it’ll work out. I’m giving DGW a call tomorrow and see what’s still available. Never hurts to have spare parts.