Rifle building question on trigger - sear relationship

[Logan1]

I'm building a Lancaster style Pennsylvania rifle and am presently inletting the trigger plate.  I'm using a double set trigger and a Siler lock.  Would someone happen to know what the clearance between the bottom of the lock sear bar and the top of the rear trigger blade should be when the trigger is set?  None of my reference material mentions this distance.

Thank you.

[Ian Pratt]

Is this for general layout purposes or do you have something specific you're trying to work out? Ton of variables here, and if this is just for general layout maybe this is a good approach - when using triggers like that what's more important is to first have enough clearance between the rear trigger UNSET and the sear. What you shoot for there is to have a little slack between the trigger and sear with both the triggers and the lock at rest. If you don't have this space, the rear trigger will hold the sear out of the tumbler notches and the gun won't hold full cock at all or just barely making the gun unsafe.

The amount of space needed is quite small. If the rear trigger is too tall you can grind some height away until the lock functions safely, and/ or you can install a backlash screw in the trigger plate to raise the "at rest" position of the mainspring which lowers the rear trigger without robbing the spring's power. If the trigger is too short leaving a big gap between it and the sear , you'd need to make an adjustment like bending the sear to reach it and/ or brazing a lift onto the trigger.

Once the space is correct , the triggers should trip the lock properly.

Quick way to check things out before inletting the triggers -  mark a spot on the outside of your lock plate showing the location of the bottom of your sear bar. Set the lock plate in the mortise. Now position your set triggers on the side of the gun lining them up as closely as you can to how they will lay when installed. If there's going to be a clearance problem you'll see it.

[Ky-Flinter]

Great info Ian.  Thanks for taking the time to share it.

Ron

[HighUintas]

I have an experience with two of those items mentioned.

When I built my flintlock, I used the Davis dst-6 and it came with very short trigger blades, presumably to put into a skinny architecture gun. My gun was more of a rocky mountain style gun made to be a little more hefty, so when the triggers were installed (I positioned them so that they were correctly placed for and aft) there was a whole lot slack to take up with the front trigger before it contacted the sear bar. My solution was to silver solder a piece of metal on top of the trigger blade to increase height. Almost no take up.

The other thing I ran into was that when I set the spring screw on the double set triggers, it was set so that the set trigger blade barely contacted the sear bar or had just barely no contact. Over time, I think think the trigger bar I let got a little compressed and then the inlet started putting pressure on the trigger mainspring. . This caused the set trigger blade to put pressure on the sear bar. I noticed that when dry firing for practice that it would occasionally fire before I pulled the trigger. Then I found it would fire by tapping on the lock with it at full cock. I took it apart and used some marking fluid to find out what was going on and realized the inlet was hitting the trigger spring! I removed the offending wood and it solved that safety problem. It could have led to a very bad accident.

[Birddog6]

Years ago I started adding to the front blade on these double set triggers.  The issue I had was when you shot it not using it as a set trigger, the front trigger took 10# pull.  That is BS. Should be 3-5# pull, not take a gorilla to pull it. To me that was poor engineering on the triggers.  The people making them were not actually Using them, they just made them.
 So adding metal to the front trigger & the angle of it made a BIG dif. To this day, I will spend a day or 2 just inletting a setting up a trigger.  One of my pet peeves I guess, having a functional front trigger, yet a good set trigger as well.  PC/HC police may not like it, but that has never bothered me at all.
And I always want a tiny bit of free take up.  Many times have seen a rifle age & all of a sudden it fires by itself or a tap on the lock or just touch the trigger & it fires.  It makes a unsafe condition.
 

[whetrock]

Years ago I started adding to the front blade on these double set triggers.  The issue I had was when you shot it not using it as a set trigger, the front trigger took 10# pull.  That is BS. Should be 3-5# pull, not take a gorilla to pull it. To me that was poor engineering on the triggers.  The people making them were not actually Using them, they just made them.

Interesting to hear how you modified them, Birddog6.
While I understand the idea of the front trigger being able to fire the gun, I've never used the front trigger for that purpose. In my experience, the main purpose of there being a trigger bar on the front trigger is that it improves the ability of the shooter to slowly and safely manually lower the cock from full cock to rest position. To put it in other words, if the cock is in full cock position and the shooter wants to release it, he has to lift the sear bar. He can pull the cock back, but if he doesn't lift the sear bar, the sear nose will just slide right back into full cock position when the cock moves forward. So he holds the cock back slightly with his thumb, then pulls on the front trigger with his index finger, so that it lifts the sear bar, moving the nose of the sear away from the full cock notch. Then he can gently release the cock to rest position. So the point I'm trying to comment on is that when doing this, the front trigger is not required to release the full pressure of the sear as from the full cock position. It's only required to counteract the pressure of the sear spring.

[Birddog6]

Allot of rifles are used for Target & for Hunting. Not everyone can afford a rifle for each.  Well, for target I like a set trigger. For hunting I want a regular trigger as lots of times I will have gloves on or cold fingers.  That is where I got to modifying the triggers to function better & easier.  No it may not be HC/PC, but I build for Me, not for judges. And I have yet to have someone gripe the triggers work Too good. Used to be, the double set triggers made for Jim Chambers had more meat up on the blade than the regular triggers. Have not bought any in years so you would have to look at them again.

[HighUintas]

Allot of rifles are used for Target & for Hunting. Not everyone can afford a rifle for each.  Well, for target I like a set trigger. For hunting I want a regular trigger as lots of times I will have gloves on or cold fingers.  That is where I got to modifying the triggers to function better & easier.  No it may not be HC/PC, but I build for Me, not for judges. And I have yet to have someone gripe the triggers work Too good. Used to be, the double set triggers made for Jim Chambers had more meat up on the blade than the regular triggers. Have not bought any in years so you would have to look at them again.

What do you do in order to drop the front trigger pull weight when using the short trigger blades? I took noticed that the force vector on the sear bar with the front trigger is such that it increases pull weight a lot. I'm not sure what mine is. Although it is crisp, it is heavy

[Birddog6]

That was the problem. As they come, takes a gorilla to pull the front trigger. Also at times too much play til the trigger engages the sear arm.  That is why I added metal & made the trigger blade taller & changed the angle of how it engages the sear arm. Then you can polish it & the sear arm & make it 100% better.

[HighUintas]

That was the problem. As they come, takes a gorilla to pull the front trigger. Also at times too much play til the trigger engages the sear arm.  That is why I added metal & made the trigger blade taller & changed the angle of how it engages the sear arm. Then you can polish it & the sear arm & make it 100% better.

Thanks. I was asking what you did to reduce the pull weight and it sounds like you changed the angle of the trigger blade. I have done a little bit of that but got tired of messing with it and I figured that anytime I'd be taking a quick shot with the front trigger without time to set it, a slightly heavier trigger is fine. I'm guessing mine is around 6 lb, which isn't too bad, but it is much heavier than my bolt action rifle.

[Wingshot]

This topic couldn’t be more well timed for me. I’m currently building an SMR and I’ve inletted the triggers only to discover the plates are too shallow. I was thinking of silver soldering some metal on the triggers to properly engage the sear. Following along with great interest.

[Birddog6]

Depends on the lock too.   I use mostly Chambers locks  & learned the angle to use & etc.
I want it angled down on front as it engages as it makes it smoother pull.

I put it in after adding to the blade & put inletting black on the tip of the blade  & wiggle it &
remove & see where it is hitting on the sear arm. Remove just a smiggen of metal & retry.  It is a slow process as you want it to just be off the sear arm & not ride it & make it fire accidentally.

I'm told Most don't mess with them & use them as they come.  I just like a lighter pull on the front.