Stuttering on half cock

[jonk]

Basically every gun that I have modified to have a lighter trigger pull- and by my count, that would be 7- has always suffered from this affliction. You solder a piece of brass onto the full cock stage of the tumbler and file it so that it releases somewhere north of 4 pounds... and, if you let the hammer down gently, it catches at half cock. Maybe not enough to stop the fall of the hammer, but enough to interrupt it.

For a long time I was frustrated beyond belief in chasing accuracy, until I noticed this, and smoothed out the half cock notch a bit too. I think the lock was falling slowly and catching just enough to throw me off.

Thing is, modifying the half cock notch is tricky business. You have to remove metal, pure and simple, and if you go too far, you've ruined the tumbler.

Anyone else find this, or have any fixes?

[John Bly]

If the sear spring is too strong then the trigger is not pulled far enough out of the notch upon release and it catches on the half-cock notch. I like the pull of just the sear spring to not be more than 2 lbs. You can check this with the hammer down. Just check how much it takes to move the trigger by itself. You can thin the sear spring to reduce the tension but work slowly. It's easy to ruin a sear spring.

[Michael Bodner]

Jonk,

You are discovering that a lighter trigger pull translates into less force/motion pulling the trigger clear of the half-cock notch. Once you reduce the normal pull you will almost certainly have to reshape the half-cock notch.

Generally, this area is not too hardened. You will have to reduce the height such that the sear completely misses the tumbler. If you don't you risk hitting the sear and shattering it. One way to determine how much to remove is to remove the sear spring which allows you to rotate the tumbler by hand once the sear releases. Then, see if the tumbler will hit the sear. If it does you can then gauge how much to reduce the height of the tumbler. Once you get it clear, then you will probably have to recreate the notch using a Dremel (thin) cut off disk.

It's pretty easy to do, but can make you nervous as you may have to take off a LOT of material to clear the sear. But don't worry. Unlike the full-cock notch, the half-cock does not affect the trigger pull. It only has to be deep enough to capture the sear and hold it there.

Good luck!!

-Mike

[jonk]

I hadn't thought about lightening the spring. It did occur to me that what was happening indeed is that with less force needed to pull the trigger off full cock, the sear wasn't disengaging as far or with as much vigor as it previously did. Hence, not entirely clearing half cock.

My current project is tuning my Potsdam lock. I lightened the full cock weight to about 5 pounds, which is fine to me; I'm not going to chase that last pound or so. But it hits the half cock BAD. It's a gun that I got, shot at a few skirmishes, and kind of set aside in favor of my 42 or 16. Now I'm getting to finishing it up.

I'll probably start by some fairly cautious re-shaping of the tumbler, and if i can get that without removing too much metal, call it a day; and only look at the sear spring as a last option.

[John Holland]

One thing you want to keep in mind if you use Bootsie's method is that you are changing the geometry of the tumbler. By lowering the height of the tumbler at the half-cock notch and then recutting the notch you have now caused the sear bar to drop lower into the lock cavity. It doesn't take much for it to drop below the edge of the lock plate. Once this happens you now have interference with the wood in the cavity. This can prevent the sear from properly engaging the half-cock notch. Depending on the timing of the trigger the sear bar can also drop low enough to rest on top of the trigger, which in turn can also prevent the sear from engaging the half-cock notch. This condition is even more exacerbated when the tip of the sear is broken off and recut, making the sear shorter. This is a common malady seen in many old original arms where the wood has been gouged out below the sear bar and the top of the trigger has been filed off.

[Kevin Tinny]

This is very good stuff; thanks:

Please tell me if this "stuttering" problem can happen with unaltered U.S. arsenal locks.
Hopefully the geometry was well developed by 1841.

Many thanks,
Kevin Tinny
42nd NY

[jonk]

This is very good stuff; thanks:

Please tell me if this "stuttering" problem can happen with unaltered U.S. arsenal locks.
Hopefully the geometry was well developed by 1841.

Many thanks,
Kevin Tinny
42nd NY

Well, after lightening the trigger pull, it can. I had it happen with my 16, 42, repro fayetteville, and repro 61.

Update: took me most of the day to get it right, as it was a case of taking it apart, putting it together, filing some more, repeat repeat... I got it where I wanted to without having to lighten the sear spring.

As a side note, while I had it apart, I compared it to an Armi Sport 61 sear spring. I think that if needed, the latter could be made to work with a slight lengthening of the lock plate retaining cut out slot, and a slight bit of removal of spring metal near the screw hole, with few other modifications.