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Old December 28, 2006, 08:13 PM   #1
A-Mac.50
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What makes a gun full auto?

Hey, so my question is what key internals differ inside say a AR-15 for example thats semi and a AR-15 that full auto capable? What internals make these rifles and most other auto rifles capable of firing full auto? Another example could also be a Glock 18 compared to say a Glock 17.
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Old December 28, 2006, 08:43 PM   #2
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It all has to do with the triggering/sear system. Semi autos have a secondary sear system that makes it so you have to release the trigger and pull it again in order for it to fire again. Full autos have the secondary sear disengage when the bolt closes into battery and then seeing as the trigger is still being pressed, the gun fires and keeps firing until the trigger is released.

This is just the laymens term of full auto fire. I appologize that I didn't elaborate more into detail.
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Old December 29, 2006, 01:01 AM   #3
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Basically the parts are all different. An AR-15 is like a dodge neon with a ferari body, it may look just like the M-16 but it is WAY not the same inside.
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Old December 30, 2006, 06:00 PM   #4
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I am one of the lucky FFL with a G18.


The difference between regular Glock are on the outside:


The selector switch and the pin on the back.

On the inside:



The longer rails and the cutout. Also the G18 slide is more narrow, so it does not fit on other Glock frames!
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Old January 3, 2007, 12:14 AM   #5
Abominable No-Man
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What Maser said is pretty close.

In a nutshell, a select fire rifle has some extra/different internal parts. Depending on the weapon in question, they will vary in nomenclature/layout/etc. A select fire M16, for example, has automatic sear and disconnector assemblies inside the lower receiver, along with the associated pins, springs, and selector switch. (Alsp, some parts, like the bolt carrier of a weapon, may or may not affect select fire capability, but are considered select fire parts as well. Be careful about what you install.)

The parts are not "drop-in": depending on the weapon in question, a different receiver template is required in order to drill the extra hole/s required in order to correctly install the parts. This is not something that is advisable to try with your Black and Decker cordless drill; it requires a high level of precision, and is illegal without a class 3 manufacturer's license.
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Old January 3, 2007, 11:54 PM   #6
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Quote:
and is illegal without a class 3 manufacturer's license.
That is an SOT 4 right?
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Old January 4, 2007, 03:01 PM   #7
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Quote:
That is an SOT 4 right?
Elucidate, please.
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Old January 4, 2007, 04:01 PM   #8
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SOT is a Special Occupational Tax. A firearms dealer pays this tax to deal in machineguns and other National Firearms Act (NFA) weapons.

Class 1 SOT = importer of NFA firearms
Class 2 SOT = manufacturer of NFA firearms
Class 3 SOT = dealer of NFA firearms
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Old January 4, 2007, 07:07 PM   #9
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Then there is the Full Auto that fires from an open bolt like the Thompson.
If your , lets say modle 100 win. was to stick a fireing pin, it will just plane empty the box...
I wouldn't want the Booze-Butts-Bang & Boom Cops to find out i made a fireing pin stick!

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Old January 4, 2007, 07:49 PM   #10
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Quote:
Then there is the Full Auto that fires from an open bolt like the Thompson.
If your , lets say modle 100 win. was to stick a fireing pin, it will just plane empty the box...
...assuming it doesn't self destruct first.

(there's a reason open bolt, full-autos in rifle calibers do not use a fixed firing pin)
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Old January 4, 2007, 07:52 PM   #11
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Of late i have to say what makes something full auto is BATFE calling it that , wheather or not they allready called it semi . LOL
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Old January 4, 2007, 09:21 PM   #12
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I read this post and was reminded of the time I bought a 22 rimfire for my wife to play with. I loaded the clip and she squeezed of a round, except, the gun went full auto. I couldn't believe it so I tried it, pulled the trigger and just a single round went off. I tried squeezing the trigger slowly and carefully as I was aiming at a small target. All of a sudden, full auto. It appeared that if I squeezed the trigger very slowly, it would somehow miss the disconnect and run full auto. Well long story short, I had some fun in the dessert for a while and later brought it to a gunsmith to have it fixed. I was a little afraid of BATF,, no E at the time. I since sold it for something else 15 years ago.
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Old January 4, 2007, 11:16 PM   #13
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Quote:
I read this post and was reminded of the time I bought a 22 rimfire for my wife to play with. I loaded the clip and she squeezed of a round, except, the gun went full auto. I couldn't believe it so I tried it, pulled the trigger and just a single round went off. I tried squeezing the trigger slowly and carefully as I was aiming at a small target. All of a sudden, full auto. It appeared that if I squeezed the trigger very slowly, it would somehow miss the disconnect and run full auto. Well long story short, I had some fun in the dessert for a while and later brought it to a gunsmith to have it fixed. I was a little afraid of BATF,, no E at the time. I since sold it for something else 15 years ago.
Was it a Stevens 87A by any chance? Mine will go in 3 or 4 round bursts every once in a while.
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Old January 5, 2007, 02:50 AM   #14
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My POS Kahr Thompson developed a "burst" capability... they fixed it after I sent it back a few times. It made me damn nervous to receive a psudo-select fire "repaired" rifle in the mail not once, but twice from a manufacturer. Of course, they never fixed its horrendous jamming issues (it was a Kahr, after all).

My buddy Art recently made my M11/9 fire a few bursts. I think he may have done it through some sort of one-in-a-million combination of limp wristing, "clawing" the trigger, and spazmatic arm movements. I have been unable to recreate this failure after another 500 rounds so I have postponed sending it off for service. If it happens again, it's off to the smith. If I wanted a full-auto I would have bought one...

These things happen.
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Old January 5, 2007, 03:38 PM   #15
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Hedley... you know, I think it was a Stevens,but I don't remember the model #.. This one would empty a complete clip of 22's. I played with it for a day and had some shoot em up fun and went through a lot of 22 ammo. I later figured I better get it fixed so I didn't get into trouble. The last time before that I was shooting full auto was with an M-14 and an M-60 in the Army.
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Old January 7, 2007, 07:17 PM   #16
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Those old Savage/Stevens 87's are known for that.
I've repaired a number of them for that problem.
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Old January 10, 2007, 07:14 PM   #17
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Quote:
What makes a gun full auto?
Money.
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Old January 11, 2007, 04:01 PM   #18
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What makes a gun full auto?

According to my dentist, filing down the firing pin will do it. I would have disabused him of the notion but I chose not to argue with someone who was about to poke around in my mouth with sharp tools. The poor guy is a typical Jersey weenie who got his firearms education from TV. Great dentist though.
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Old January 16, 2007, 08:29 PM   #19
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Disconnector

Basically, no matter what the design (other than open bolt fixed firing pin), the difference involves how the disconnector functions. The disconnector is the piece which functions to keep the gun from firing out of battery. On semi auto guns, the trigger stays disconnected until released, then it resets. On select fires guns in the auto mode, the disconnector releases when the gun return to battery, and since the trigger is still pulled, the gun fires.
Different designs do this in different ways, but this is the principle.

Open bolt guns function differently. The bolt is held to the rear until the trigger is pulled, then goes forward, chambering a round and firing it. This cycle repeats until the trigger is released, then the bolt is caught in the rear position. Most SMGs and many belt fed guns use a variation of this system.

The AR 15 has undergone an "evolution" in it's internal parts since it first came out. Original Ar-15s had the same internal parts as the M16 rifle, except the auto sear was not installed. Over the years, the design has been changed so that none of the current AR fire control parts are the same as the M16's. There have in fact been people arrested and taken to court for having one of the M16 parts in their rifle. The Feds said that was a machine gun. They have no sense of humor. The AR will not function full auto unless all the fire control parts are the correct ones for full auto fire. An M16 hammer will not let the gun fire full auto, but the Feds don't seem to care. They will prosecute any way. Some people have even been prosecuted for talking about it. It is a wonderful thing to live in a free country. I wonder where that might be?
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Old January 16, 2007, 08:39 PM   #20
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Afterthought

What makes a gun a machine gun?

Original legal definition was "fires more than one round for each pull of the trigger". Since the 1980s, the Federal Govt has declared certain gun parts (whether in a gun or not) in and of themselves to be legally machineguns.

So, for legal purposes, whatever the Feds say is a machinegun is a machinegun, even if it a piece of steel with less than a cubic inch of volume. Same license required to legally own, same legal penalties if not licensed (10 years+$10K+ fine).

Whatever the Feds say is a machinegun is a machinegun, unless you can convince a court otherwise. Not an easy or cheap thing to do. And it carries some risk as well, should you fail to convince the court. Not recommended.

Hope this helps.
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Old January 18, 2007, 12:38 PM   #21
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Acording to the BATFE, a shoelace:

http://www.mp5.net/info/ATF_Ruling_2...ring_Trick.pdf
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