Hello Everyone,
I have had the privilege of being able to shoot various firearms during my life. My favorites have been the M1 Garand and the AR-15, with my all time favorite rifle being the M1 Carbine. Of course there have been various shotguns and pistols along the way as well. The question I have is with all of the guns that I have fired, the trigger mechanisms work pretty much the same way. You pull the trigger and that in turns moves various components to fire the rifle. What I can’t seem to visualize is how the trigger mechanism works in a machine gun like the Browning .50 caliber or the smaller .30 caliber. From what I have seen in pictures and films it appears that the trigger is a button on top of the grip handle. I know that it isn’t an electrical trigger like in a mini-gun, so it must be mechanical, but I don’t understand how it works. You are pushing down on the button with what seems like very little force. When you pull the trigger on a rifle you can physically see it moving backward and imagine it in turn moving another piece inside the rifle. I can’t seem to visualize how lightly pushing a button “triggers” the action to fire the machine gun. So, in simple turns, what happens when you push the button?
It’s still just a trigger. With a semi-automatic rifle like an AR-15 you have to manually cock the firing mechanism before the first shot, after that the recoil and/or gas pressure from the bullet is used to reload and re-cock it. It’s exactly the same with a fully automatic rifle, the only difference is that the full-auto mechanism will go the extra step of releasing the firing pin again if the trigger is still held down. It’s actually only a pretty small difference between semi and fullly automatic, mechanism wise.
Thanks, I get the part about the releasing of the firing pin in fully auto mode. I don’t know if I am explaining my question correctly or not. What I want to know is what happens when you push the fire button on the grip. The motion of the “push” is vertically down, not horizontal. When the button is pushed does it rotate a lever that releases the firing pin? I don’t see how the vertical action corresponds into the mechanics of operation the firing pin. A trigger pull on a rifle is usually required a bit of effort to move the mechanical pieces to put the firing pin into action. There seems to very little effort on the initial press of a machine gun button. I realize that once the first round is fired, the automatic cycle of the gun takes over, it is the initial action that confuses me. Speaking of confusing, I apologize that I am probably not phrasing the questions properly. That’s what I get for not being able to sleep again!
Whether the trigger is horizontal or vertical doesn’t matter much. When you pull the trigger, you release the trigger sear. The trigger sear puts the rest of the cycle in motion and has a spring to put it back into its original position if you release the trigger.
This animation can give you an idea, although it details a closed bolt mechanism, the part about the trigger and trigger sear can be seen
In a closed bolt mechanism* like the M16, the trigger sear releases the hammer which strikes the firing pin which strikes the round’s fuse. In an open bolt design* like the M2, the trigger sear releases the bolt group which serves as a firing pin in addition to shoving the round into the chamber.
*Typically, this is subject to inventiveness of weapon designers.
The first action is that the weapon is cocked - this stores energy in a spring on the firing mechanism. The trigger sear engages in a notch, preventing it from moving forward to activate the firing pin. The sear is quite small, so it only takes a small movement to release the bolt. Everything else (trigger or button) is just some mechanics to produce the required motion, feel and safety to release the sear - trigger pull pressure for a rifle, simple down pushbutton on a machinegun. A few more mechanics allow for fire selection (single, triple, full auto).
Oh, and (mechanically) the sear does not have to be in any particular position - under/over/side of the bolt all seem reasonable. However, preventing the sear from dropping/slipping accidentally is a major factor in firearm design - for many firearms, the sear cannot move to release the firing mechanism if the trigger is not pulled, preventing accidental discharge from impact.
Pistol triggers are more complex, as the double-action can cock the weapon before the trigger sear drops.
Interesting fact - John Browning designed his firearm mechanisms in two dimensions. He sketched his design on card, and cut it out. He could lay out the entire mechanical design in this way, then had his brother Ed machine the parts with thickness being specified along the way. (cite by Martin Gardner).
Si
The M2 fires from the closed bolt.
[nitpick] should be “the round’s primer” [/nitpick] but you knew that.
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Thanks. I thought it was like the M240 or M249 and most other machineguns and lazily didn’t look it up. How does it prevent overheating and cockoffs as a closed bolt weapon?
Thanks. Bad translation on my part.
A heavy ass barrel, and a spare heavy ass barrel. That’s about it, unfortunately.