Would a newly made open bolt semi auto be an MG?

[Dreamcast270mhz]

I've had an idea for a while of picking up a parts kit from the various open bolt MGs and making an open bolt semi auto. Until I heard about how the ATF doesn't like that. So for example, I make a Bren gun from a parts kit, reweld the receiver etc. but decide to make it open bolt. Have I just in a legal sense made a Machine Gun? If so then the ATF has lost all common sense.

 

[Ian]

Yes, you have.

 

[Sam1911]

You would have to apply for a design review by the ATF's Tech Branch to answer that question definitively -- but any time you're building a new, one-off semi-auto design you should do that -- but the answer is almost certainly yes.

Open bolt semis are generally one bent wire or creatively misplaced paperclip away from full-auto fire. A little too close for the ATF's comfort.

 

[bobbo]

Yup. It's a machine gun. Open bolt is very easy to modify to full-auto, and to modify back. The ATF isn't insane (about this one particular facet of regulations, for a change), it's covering their butt. The bent paperclip away comment is right on.

 

[Quiet]

In 1982, the BATF ruled that open bolt semi-auto firearms will be classified as MGs because...

The National Firearms Act, 26 U.S.C. 5845(b), defines a machine gun to include any weapon which shoots, is designed to shoot, or can be readily restored to shoot, automatically more than one shot, without manual reloading, by a single function of the trigger.

The “shoots automatically” definition covers weapons that will function automatically. The “readily restorable” definition defines weapons which previously could shoot automatically but will not in their present condition. The “designed” definition includes those weapons which have not previously functioned as machine guns but possess design features which facilitate full automatic fire by simple modification or elimination of existing component parts.

Open bolt semi-auto firearms made before 1982 are "grandfathered in" and not subject to the MG classification.
All open bolt semi-auto firearms made after 1982 are considered MGs and are subject to the National Firearms Act.

 

[Flfiremedic]

What pre 1982 subguns were open bolt? Typical prices?

 

[Remo223]

I think they were typically 22 long rifle. But I can't remember for sure.

 

[Sam1911]

What pre 1982 subguns were open bolt? Typical prices?

Subguns? Almost all of them.

A partial list:
American-180, Carl Gustav M/45 (Swedish K, S&W M76), Jatimatic, M3, MAC-10 & 11, MP40, PPSh-41, Sten, Sterling, Suomi M-31, Thompson, Uzi.

I know there are more, but I'm forgetting some.

Prices? All over the map. Some MACs are going for in the $4K range. Some vintage Thompsons with history sell for $30K+.

 

[Flfiremedic]

Oops...no proof reading...what semi autos were open bolt prior to 82, and are the prices through the roof now?

 

[Sam1911]

Ahhh, I see. Well, lots of semi-auto versions of the SMGs mentioned above. Many of them had to be heavily redesigned to have a real firing pin and hammer or striker so they can fire from the closed bolt position.

Also the various semi-auto sub-guns-lookalikes like the old Intertech guns that evolved into the TEC-9 and related guns. The first American made version (KG-9) fired from the open bolt, but was a semi.

Opening up an open-bolt gun is kind of surprising. Generally there's "nothing" inside. Just a bolt with usually a fixed firing pin or just a firing pin nub machined into the breech face, a big spring, and a trigger mechanism in the grip.

The trigger mechanism doesn't do anything but get out of the way when tripped. Just keeps its head down and lets the bolt fly back and forth. Hard to imagine a simpler mechanical device.

 

[Flfiremedic]

Yeah I'm pretty familiar with the open bolt MGs and SMGs, but just can't remember what was semi auto and open bolt 19 + years ago. Would be interesting to have one, but no idea what weapons to look for or prices.

 

[4thPointOfContact]

At one time, Cobray tried to market such a device (pretty much as a big Foxtrot Yankee to the ATF.)
Consider that the ATF ruled an open-bolt, semi-auto, Single Shot shotgun was prohibited, what do you think they'll think about what you may have done.

 

[DoubleTapDrew]

Oops...no proof reading...what semi autos were open bolt prior to 82, and are the prices through the roof now?

The most prevalent one I can think of was the semi auto MAC series. I don't know what you consider "through the roof" but IIRC open bolt semi auto macs typically go for double what a closed bolt one does ($600+). However compared to an open bolt full auto mac ($3000+) I guess it could be considered a bargain.