lock and trigger function

[54Bucks]

 Before I get into the subject let me lay some groundwork for it. For over thirty years I've used double lever set triggers. No need to make this a discussion about the merits of a single over a double or vice versa. Whether I'm shooting at a ten ring or a ten point, a set trigger is what feels right to me. I've also learned how to keep my fingers warm and deal with that little snick sound.
 I've never adjusted my set trigger assemblies to what anyone would consider hair. As I like to feel the trigger without chance of the gun firing.I've tried a few guns with single triggers yet even a crisp single trigger with no excessive travel is a problem due to the ammount of pressure before it breaks. For me that additonal pressure is as problematic as a lighter single trigger with excessive travel when you are as conditioned as I am. But I guess I'm also stubborn as I'm still trying to talk myself into a single trigger on the next one I'm planning.
 So I've started to look closer at lock function and single triggers with the idea of getting a lighter trigger pull for a single. What strikes me so far is how critical ideal lock function is! We can debate the ideal pin location of a single trigger but........it sure appears the actual geometry of the tumbler notch/sear nose engagement is the target. At this point I also think the mainspring loaded tumbler at full cock has more affect regarding a trigger pull weight than the sear spring does. No doubt there are countless bearing points in a lock ,like resistance from excessive sear/bridle screw pressure to consider when trying to achieve optimum lock trigger function. Makes me think lock tuning should be in the tutorial section and lock inspection and tuning should be mandatory on any build.
 I don't like the idea of simply having the engagement point (tumbler to sear nose)honed  so shallow that it feels light but is actually on the edge of danger. Perhaps there is actually no other way to get a single trigger to have the trigger feel I'm used to.(guessing 2-3 lbs.)

[D. Taylor Sapergia]

Reducing the depth of the full cock notch certainly reduces the "creep" in the let-off.  You have to be able to push on the cock at full bent without it firing.  Polishing the surfaces, while still keeping them sharp and square, further lightens the pull.  Four pounds is a maximum for me, for a simple trigger.  I have achieved less than a pound, but it's pretty hairy, and not necessary.

[WadePatton]

Thanks for bringing this up, as I too like 'em light and clean.  I didn't understand how the double sets actually functioned until buying the one for this build.  I had used them, but now I "get it" fully.  I cleaned up the lock before purchasing the trigger -as if I were working on a modern where every little friction is part of the sum of the pull.  I also don't want things "wearing in" and changing geometries/feel unnecessarily.

WRT Lock function, the supplier I got my lock from seemed a bit perturbed that I (mentioned it to him in person) took the lock apart and cleaned up the surfaces (all mating)--which did indeed need it according to my gentle grasp of friction and metals and triggers/sears.

That said, I now understand how a set trigger would simply "power-through" these uglies, as well as explains why/how un-set pulls (of my limited experience) have heretofore been, in a word-nasty.

I too am glad to learn that a clean and light pull on a single can be had with proper workmanship--for the time when i build a rifle for which a single is deemed appropriate.

[bgf]

Rather than hone the surfaces perhaps dangerously close, I suppose you could add some sort of takeup adjustment, which would at least allow you to keep it safe with wear.  Some of the CVA locks actually have that (yes, I know I'm going to regret saying this) and it works pretty well to lighten the pull and still maintain safe engagement as long as it is checked occasionally -- they probably need it especially because the trigger is pinned so low down on the plate.  Perhaps something like that and careful attention to geometry, etc., would get you what you need.

[A.Merrill]

     Back in the 70's, Robbins locks had a Allen screw that screwed into the tumbler and if I remember right, you could screw them in or out for however deep you wanted the sear to set in the full cock notch. I have two of them somewhere I never used, hope their not in the basement, that could be a bad thing.    AL

[brobb]

I once put a mild steel "peg" into a tumbler just in front of the full cock notch.  The purpose was to reduce the depth of engagement of the sear.  I fastened the peg in place with locktight and adjusted by filing the length of the peg.  This "fix" worked  and got me where I wanted to go.

Bruce Robb

[Acer Saccharum]

Set triggers allows the use of a rough lock. Single trigger, you gotta go thru the whole thing and polish all bearing surfaces, get just the right angles to the sear and notch. Also the sear spring tip should bear right up as close to the sear pivot as possible.

As an important safety note, the gun should hold full cock without a sear spring. Then you know the sear/tumbler angles are safe. The spring is there just to pop the sear into the notches, not to hold it there. Should the sear spring ever break, you don't want the gun going off. With a broken spring, the gun won't re-cock.

Tom

[Pete G.]

Keep in mind that when the full cock notch is cut down to reduce creep that the sear releases at a lower point in the cycle. This may or may not affect whether the half cock notch bangs into the sear. Yes, the detent is supposed to alleviate this, but keep in mind that all the parts work together. Modification to one usually requires modification to all the keep the relationship working correctly.

[Dphariss]

If you have such a thing look at the sear size and notch depth on a real or repro SAA colt or one of the better Colt C&B revolvers or copies.
The depth/contact point need not be that small/shallow. But the depth will need to be close for a really good trigger. The sear notch need not be deeper than the sear nose. If the sear nose is too deep then it can be thinned as well. Deep notches make for creep
If the FC is really deep it may be necessary to shim it to bring the sear engagement down. I prefer a  hardened and tempered screw threaded into the tumbler for this. Other wise problems with the 1/2 cock and/or fly can arise.
The angle on the sear nose and the angle of the FC notch are critical to a good single trigger pull. The FC notch must be cut to an angle that ALMOST matches a radius off the sear screw.
The sear should stay in the notch under full mainspring pressure with no sear spring. So there has to be a slight angle change from the sear screw radius. This does 2 things. It keeps the lock in full cock and lets the sear "break" out of the notch. If the sear slides out the trigger will creep if its to firmly captured it will be very heavy. Some are cut to a mini 1/2 cock form to capture the sear nose as then come from the factory, this is common in the SAA colt style lock work. But if this ledge wears off things can change dramatically and the lock work may become unsafe.
Tumblers with a steeply angled FC actually require the sear to force the tumbler back against the mainspring (in extreme cases its possible to see the hammer/cock move backwards). This makes for a really heavy trigger. So the angle must be stoned back slightly

We want a very smooth notch and sear nose that captures the sear just enough that the mainspring pressure holds the sear in but when the pressure on the sear arm reaches a certain point the sear pops out of the notch. Clean break trigger.
IE it must take more pressure to move the trigger than that required for the sear to compress the sear spring. If the sear spring is too strong the best sear/notch angles will still seem creepy since it takes too much pressure to move the spring.
So lighten the sear spring so it still gives a good sharp click when cocked. How to test? Compare the trigger pull WITH A GAGE at full cock to what is required to compress the sear spring. IE measure the trigger pull  with the lock at rest as well. If they are the same the spring is too strong. DO NOT lighten too much. This will make a DANGEROUS lock. Also a too weak sear spring will not properly operate the fly in some locks.

When all work is done and the lock installed in the gun then the "mallet" test. the lock should stand 3 light-moderate whacks anywhere on the gun (except on the hammer screw)  with 4-5oz dead blow or rawhide mallet.
If not I do not consider it safe. I had a single trigger Sharps match rifle years ago with an 8 ounce trigger that would pass this test. But this rifle was a dedicated match rifle. A lock that will not pass this test has an error in the notch angle or the sear nose angle.

Hunting rifles need to be about 4 pounds. Lighter than 3  in a field gun is getting pretty flakey.
Set triggers if really right should stand a whack or 3 as well but set triggers are sensitive to direction due to inertia of the firing trigger.

BTW placing the trigger pivot point too close the to sear bar can make a creep free trigger far more difficult to obtain.
Its possible to get a good pull with a 3/4" difference. Getting a good trigger with a 3/16" distance is actually more difficult since it requires so much trigger movement to get the sear to move.
 This work is best done with stones. I use the small square and 2 square ceramics sold by Brownells.

If you have ANY doubt about your ability to do lock adjustment LEAVE THE LOCK ALONE.
It is far easier to screw up the lock than it is to make a good trigger pull.
Hope this makes sense.
Dan