I thought this would be the best place to ask this. I know how semi-auto and full-auto guns work, but something I don't get is how select fire works. Is the watchamacallit that sticks out at the bottom of the disconnector raised up? What?
Select Fire
- Thread starter miatchguy
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Hkmp5sd
Member
"Select Fire" means the weapon will fire either semiautomatic or fully automatic, ie select fire. In semi- it lets the disconnector catch the hammer and you must release the trigger for it to be released. In full auto, the disconnector doesn't catch the hammer, so it keeps shooting as long as the trigger is held.
Hkmp5sd
Member
Oh, sorry. On the M16, in semi-automatic, the disconnector catches the hammer. When the trigger is released, the disconnect releases the hammer and the trigger sear holds the hammer back until the trigger is pulled again.
In full auto, there is a cam on the selector switch that prevents the disconnector from catching the hammer. The auto sear holds the hammer back until the bolt carrier hits the auto sear as it reaches battery. That releases the hammer, which makes it go bang and when the bolt comes back, the auto sear again holds it until the bolt goes back forward. When you let go of the trigger, the auto sear still releases the hammer, but the trigger sear engages it and holds it back.
In full auto, there is a cam on the selector switch that prevents the disconnector from catching the hammer. The auto sear holds the hammer back until the bolt carrier hits the auto sear as it reaches battery. That releases the hammer, which makes it go bang and when the bolt comes back, the auto sear again holds it until the bolt goes back forward. When you let go of the trigger, the auto sear still releases the hammer, but the trigger sear engages it and holds it back.
Hkmp5sd
Member
Badger Arms
Member
Badger Arms
Member
I didn't realize that searches expire. Yes, just click on Full Text and then click on Images to see the patent. If you really dig into the pictures and zoom in on the details, you can see how the selector merely blocks the disconnector and prevents it from catching the hammer each time thus allowing the full-auto sear to engage the hammer and trip each time the bolt flies home. The selector placed in semi-auto disengages the auto-sear and allows the disconnector to do its job. Just read through the patent.
bountyhunter
member
FWIW: there's a nice warm cell in Leavenworth for people who modify existing AR-16's per the diagram to make them "select fire" guns.
bountyhunter, I am just shocked - SHOCKED! - to see you suspect a loyal THR member of considering such a thing! 
But isn't Leavenworth an Army prison?
BTW, miatchguy, if you are ready to go the civil disobedience route, more power to you. If not, uh, don't. Those BATF boys are reeeely serious about them kind of modifications.
'Course, there's no law agin curiosity.
But isn't Leavenworth an Army prison?
BTW, miatchguy, if you are ready to go the civil disobedience route, more power to you. If not, uh, don't. Those BATF boys are reeeely serious about them kind of modifications.
'Course, there's no law agin curiosity.
Hkmp5sd
Member
miatchguy hasn't said anything about illegally modifying a firearm. He just asked how select fire mechanisms function.
SDC
Member
It depends on the design of the specific firearm you're asking about, but the principle is usually the same between general types; for open-bolt submachineguns, all the trigger does is release the bolt to fly forward. When the firing-pin fires the cartridge, the recoil forces the bolt back to extract and eject the empty case, and if the trigger is still held back, the bolt just keeps "bouncing" against the recoil impulse, like a pogo stick. If the mechanism is set on semi-auto, during its travel, the bolt knocks part of the trigger mechanism off of a step to allow the sear to spring back up and re-engage the bolt when it comes back far enough during recoil. If you're talkiing about something like the M16 or AK-47 series, there are actually two separate sears, one for semi-auto fire, one for full-auto fire (usually, the full-auto sear engages a sear-step at the far end of the hammer from its pivot pin. For example, when the M16 is set on full-auto (imagine an M16A1, without the 3-round burst for a minute), the semi-auto sear holds the hammer on "cocked" at the front of the hammer until you fire it. When you fire it (and hold the trigger back), the hammer is caught and held by the full-auto sear at the rear of the hammer, which is released automatically by the bottom rear of the bolt carrier when the bolt goes back into battery with a new cartridge from the magazine. (Something has to hold the hammer cocked while the bolt is closing, otherwise you'd get a "click" instead of a "bang", when the hammer falls way too early, or you'd get a "BOOM" from an unlocked ignition, when the hammer falls slightly too early.) It's simpler than it sounds, but I hope this gives you an idea of what's going on.
I will give this a shot. One point to remember. On any powerful cartridge, the bolt has to be closed and locked before the round is fired, and firing has to be positive. (Just a hammer following the bolt down won't work, at least not reliably, so "filing the sear" won't create reliable full auto fire no matter what some writers say.)
This describes the action of the M16 (old type without burst fire)
OK. With the bolt closed and locked, and the selector set to full auto, the trigger is pulled. The hammer falls, the rifle fires, the gas comes back through the tube and hits the bolt carrier. This moves the carrier back, which rotates the bolt to unlock it. The empty case is ejected, and the carrier continues backward. The carrier cocks the hammer down past the normal (semi-auto) sear, but with the selector set to full, that sear is held out of the way and it does not engage the hammer.
Meantime, the carrier reaches its stop, and its spring reasserts itself and moves the carrier forward, stripping a round from the magazine and forcing it into the chamber. The hammer tries to follow the carrier, but is caught by the auto sear, and held as the carrier goes forward. When the bolt is fully turned and locked, the carrier still has a short distance to move, and it is during this movement that the rear of the carrier pulls forward on the top of the auto sear, rotating it out of engagement with the hammer and allowing the hammer to fall and fire the newly chambered round. This continues until the trigger is released or the magazine is empty.
In semi-auto, the selector cam allows the semi-auto sear to catch the hammer every time, so a pull of the trigger is required to fire the rifle. The auto sear is always moved by the carrier going forward, but in semi-auto fire, it is not holding the hammer and is out of the way when the hammer falls.
Note that this describes the old semi/full rifle, not the M16A2 with the burst control. That system is just too darn complicated to describe without
pictures.
Jim
This describes the action of the M16 (old type without burst fire)
OK. With the bolt closed and locked, and the selector set to full auto, the trigger is pulled. The hammer falls, the rifle fires, the gas comes back through the tube and hits the bolt carrier. This moves the carrier back, which rotates the bolt to unlock it. The empty case is ejected, and the carrier continues backward. The carrier cocks the hammer down past the normal (semi-auto) sear, but with the selector set to full, that sear is held out of the way and it does not engage the hammer.
Meantime, the carrier reaches its stop, and its spring reasserts itself and moves the carrier forward, stripping a round from the magazine and forcing it into the chamber. The hammer tries to follow the carrier, but is caught by the auto sear, and held as the carrier goes forward. When the bolt is fully turned and locked, the carrier still has a short distance to move, and it is during this movement that the rear of the carrier pulls forward on the top of the auto sear, rotating it out of engagement with the hammer and allowing the hammer to fall and fire the newly chambered round. This continues until the trigger is released or the magazine is empty.
In semi-auto, the selector cam allows the semi-auto sear to catch the hammer every time, so a pull of the trigger is required to fire the rifle. The auto sear is always moved by the carrier going forward, but in semi-auto fire, it is not holding the hammer and is out of the way when the hammer falls.
Note that this describes the old semi/full rifle, not the M16A2 with the burst control. That system is just too darn complicated to describe without
pictures.
Jim
Hkmp5sd
Member
There is an easy way to learn how a machinegun works. Buy one! Take it apart, put it together and shoot it. Better than any description, diagram or animation. More fun too!
Gun Plumber
Member
I HATE to be a BUZZKILL, but
THERE IS a law on the books of discussing HOW TO MODIFY weapons that were ONLY designed to shoot semi. Best lock this one off and delete it to keep everyone from getting a call from ATF.
THERE IS a law on the books of discussing HOW TO MODIFY weapons that were ONLY designed to shoot semi. Best lock this one off and delete it to keep everyone from getting a call from ATF.
Badger Arms
Member
No there isn't. This discussion was about how a military fully-automatic weapon works. The 1st amendment protects free speech. We were speaking with a 15 year old explaining how something works. Which law are you referring to that limits this type of speech? This person could join the Marine Corps in a little over a year. Where in here did it suggest that anybody wanted to modify a semi-auto weapon to shoot fully-automatic?
Gun Plumber
Member
Whatever you say, but ATF...
I'm sorry, but you WERE DISCUSSING CYCLE OF OPERATIONS of a semi-auto to select fire in this thread. And while you might win a Supreme Court case re:1st Amendment, the ATF DOES TAKE an extremely dim view of discussing such things over the net.
Don't believe me, call them. You will get an earful. And maybe your eyes opened.
But hey, ignorance IS knowledge, right? I have worked for several class 3 or class 10 people and I PROMISE YOU NONE OF THEM would join this discussion on a bet.
And the ONLY PROOF you have that you are ACTUALLY talking to a 15 year old is his say so. Can we say STING OPERATION? Duh, happens all the time over the net.
I'm sorry, but you WERE DISCUSSING CYCLE OF OPERATIONS of a semi-auto to select fire in this thread. And while you might win a Supreme Court case re:1st Amendment, the ATF DOES TAKE an extremely dim view of discussing such things over the net.
Don't believe me, call them. You will get an earful. And maybe your eyes opened.
But hey, ignorance IS knowledge, right? I have worked for several class 3 or class 10 people and I PROMISE YOU NONE OF THEM would join this discussion on a bet.
And the ONLY PROOF you have that you are ACTUALLY talking to a 15 year old is his say so. Can we say STING OPERATION? Duh, happens all the time over the net.
Badger Arms
Member
No, we weren't. You might be ignorant of the workings of a selct-fire weapon so let me inform you just in case. A select-fire weapon is one which can, through some means, fire either semi-automatically or fully-automatic. The cycle of operations on an M-16, the weapon referred to in the patent I cited, is to move the selector from semi to full. That's not a conversion, it changes from semi-auto to full-auto modes in a selective-fire weapon such as the M-16.
I live in a state where we can own a fully-automatic weapon and many MIGHT want to know how they work and discuss them. Said discussioin does not violate any law.
What does it matter WHO I am replying to? You can find the information being discussed here on the government web site I referenced above. It's patented and available free to the public. I don't care if the poster of this question is a 3-year-old, this is public knowledge, public information, and academic at best.
Again, I challenge you to quote from the previous posts where anybody suggested that any conversion of a semi-automatic-only firearm was going to take place, was contemplated, or otherwise. Every substantive reply to this thread has described how a legal selective-fire gun works.
Well, I have called them. In fact, I called them most recently about NFA definitions for rifled shotguns. I found them to be very helpful and informative, and professional. They did not hunt me down, stomp my cat to death, and shoot my wife in the head. In fact, they did not know the answer to my question immediately so they researched it and called me back. I don't feel the need to call them this time because I know there is no law that says you cannot talk about guns. In fact, it's an absurd statement. Please quote the law you are referring to. I'd love to read it.
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