Zonie posted some data about double set, single throw triggers and compared them to double set, double throw triggers. A good percentage of what was posted, I am in tune with. I am however miffed at why double set single throw triggers do not need a fly in tumbler. In my mind (here is where I need help) the resulting effect on the sear with either single or double throw triggers is the same. The question really is : Why don't both types of triggers need a fly?
Flintlocklar
I'll try to answer your question but in order to do it I will need to explain what happens with each type of set trigger and for those people who don't quite understand what the parts of the lock do, give a description of their names and how they work. You old timers will have to bear with me on this.
First some descriptions of the parts.
The tumbler is the part with the full cock notch in it and usually it has a half cock safety notch to keep it from rotating. The tumbler is the part that the mainspring pushed on to rotate it. The hammer or flintlock cock is attached to the tumbler on the outside of the lock plate.
The sear is a movable part with a small, hardened end on it. The nose end falls into the half cock or the full cock notch on the tumbler to keep it from turning. If it is moved slightly to disengage from the half cock or full cock notch, the tumbler (and hammer) will rotate toward the fired position. The part that moves the sear is the trigger which usually has a blade on its top to push on the "arm" of the sear to make it disengage from the tumbler notches.
There is a small spring that pushes the sear nose against the tumbler so that it will snap into the notches in the tumbler. When the trigger is not pulled, the spring keeps the nose of the sear snugly against the outside of the tumbler.
OK. When you pull the hammer or cock back from the fired position the tumbler starts to rotate and the mainspring gets bent. As the hammer is brought back further, the sear spring pushes the nose of the sear into the half cock notch. This half cock notch has a U shape to it to trap the sear nose and after the sear has entered it, if you allow the hammer to move slightly forward, the nose of the sear becomes firmly trapped in the U shaped notch. The gun is now at half cock.
Pulling the hammer back further allows the nose of the sear to pull out of the half cock notch but it's nose is still snugly against the outside of the tumbler.
When the full cock notch on the tumbler gets to the nose of the sear, the nose snaps into the full cock notch. Releasing the pressure on the hammer, the nose of the sear holds everything in place. The gun is now at full cock and ready to fire.
Now, for the triggers:
With a simple trigger, when the finger tries to pull it, the forces on the nose of the sear in the full cock notch plus the sear spring's pressure try to keep the sear from moving. This means the trigger finger has to pull harder on the trigger before things start to move.
As more finger pressure is applied, the sear nose starts to slip on the full cock notch and finally pulls out of the notch. This releases the tumbler and the hammer starts to fall.
Because it took quite a bit of force to let the sear slip out of the full cock notch, while the tumbler starts to rotate, the finger pressure continues to move the sear away from the tumbler. As the half cock notch whizzes past the end of the sear, the sear is well away from it so the tumbler continues to rotate and the hammer continues to fall until the hammer hits the cap or the cock hits the stop shoulder that stops it from traveling further down.
With the double set, double throw (or blade) set trigger,
if only the front trigger is used without setting the rear trigger, the trigger and the lock works just like the simple trigger did. Like the simple trigger, there is a blade on the top of the trigger that pushes up against the sear arm and releases it. Also like the simple trigger, the heavy finger pressure keeps the nose of the sear well away from the tumbler as it rotates under the nose of the sear.
Now, getting to firing the double set, double throw trigger.
With this type of set trigger, there is a blade on top of the rear "set" trigger. Normally, with a double set, double throw trigger, this rear trigger blade does not touch the sear arm. Because neither it or the blade on the front trigger is touching the sear arm just pulling the hammer back to full cock allows the sear nose to engage the full cock notch.
As I mentioned the rear trigger"s (I'll call it the "rear" trigger because that's easier) blade normally clears the sear arm but after it is "set" the spring loaded trigger blade is now standing a considerable distance from the sear arm. Due to its design, the latch that holds the rear trigger in the set position only needs a small amount of pressure to release the catch and to allow the rear trigger to snap forward.
When it is released, the spring rapidly accelerates the trigger and its top blade rapidly toward the sear arm. When the blade hits the sear arm it knocks the nose of the sear out of the full cock notch.
As soon as it hits the sear arm, the triggers blade bounces off of the arm. When this happens, in less than the blink of the eye, the sear spring pushes the nose of the sear back against the outside of the tumbler. This happens so quickly, the half cock notch has not rotated to the location of the nose of the sear. It is still approaching it.
Now, without something in the way to prevent the nose of the sear from entering the half cock notch, when the notch does get to the nose of the sear, the nose will enter the notch and everything instantly comes to a halt. In the best case, the gun just won't fire. In the worst case, the hard nose on the sear will shatter and the hardened half cock notch ledge will break off making the "U" shape into a "L" without a way of safely holding the sear in the "half cock" position.
The answer to keep this from happening? The
Fly.
If we can put something at the mouth of the half cock notch that will get out of the way when the hammer is raised from a fired position and allow the nose of the sear to enter the half cock notch, the gun can easily be set at half cock.
If this same something will get
in the way of the nose of the sear when the hammer is falling from full cock it can keep the sear from catching in the half cock notch and the hammer will continue to fall and fire the gun. That in a nutshell, is what the fly does.
If the nose of the sear tries to enter the half cock notch as the hammer is pulled back, the fly gets out of the way and allows it to happen. When the lock is released from a full cock position, the fly gets in the way and the nose of the sear hits it, bounces up over the top of it and then returns to its spring loaded place against the side of the tumbler as the tumbler continues to fall.
OK. Now, what if the lock doesn't have a fly in the tumbler but you want to have the easy trigger pull and speed of a set trigger?
The double set, single throw trigger is the answer.
The single throw set trigger is a spring loaded trigger just like the double throw trigger is. It has a blade on top of it just like the double throw trigger so, what if we made it so that this blade was always pushing up on the sear arm whenever it was in the "unset" condition?
If we did this, with the rear trigger in the set position, its top blade would be clear of the sear arm so we can cock the gun to a full cock position.
When the rear set trigger is released it would knock the sear out of the full cock notch
but because it is always pushing on the sear arm when it isn't cocked, it will keep the nose of the sear well clear of the outside of the tumbler as the half cock notch whizzes past it. Just like the heavy pull of the trigger finger did with a simple trigger setup.
Now, if we do use this idea, because the rear trigger blade is always pushing up on the sear arm whenever it isn't set, there is no way to cock the gun without first setting the rear trigger so, the front trigger can't fire the gun all by itself so, there isn't any reason for the front trigger to have a sear release blade on it.
Hope this all makes sense to you folks.
