All open bolts machine guns?

johnwilliamson062 · May 6, 2013, 11:01 PM

I have been surfing the web looking at home made designs the last few days. I have seen a number of questionable designs. Maybe foreign made or maybe my eyes aren't accurate at measuring. One thing I have seen is single shots that fire from an open bolt. I was wondering if the prohibition on open bolts is limited to repeating arms, or if these items are illegal.

Madcap_Magician · May 7, 2013, 08:15 AM

Is there a prohibition on firearms firing from an open bolt? I am not aware of one.

The only real reason to have a firearm fire from an open bolt is to aid cooling for moderate to rapid sustained automatic fire. I can't imagine what the point of a single-shot firing from an open bolt would be.

musher · May 7, 2013, 08:31 AM

Quote:

I can't imagine what the point of a single-shot firing from an open bolt would be

simplicity of the firing mechanism.

cslinger · May 7, 2013, 08:56 AM

Yes, if it fires from an open bolt it is an easily convertible machine gun in the eyes of the ATF. Don't build or buy one unless you are licensed to build or it's a Pre 84 papered gun.

musher · May 7, 2013, 09:35 AM

Quote:

Yes, if it fires from an open bolt it is an easily convertible machine gun in the eyes of the ATF. Don't build or buy one unless you are licensed to build or it's a Pre 84 papered gun.

I wonder how this could be true for a single shot with no provision for a magazine.

**Mike Irwin** · May 7, 2013, 09:45 AM

yep, firing from an open bolt is about as simple as it gets.

Most often in such a design the "firing pin" is just a bump on the bolt face -- nothing mechanical about it. In effect, it's a slam-fire gun.

There is something of an art to balancing the weight of the bolt, the power of the cartridge and the power of the main spring to make sure that the system is in balance and that the cartidges don't pop early, or not at all.

**Mike Irwin** · May 7, 2013, 09:46 AM

"I wonder how this could be true for a single shot with no provision for a magazine."

I THINK Savage made such a rifle years and years ago.

Skans · May 7, 2013, 10:59 AM

Generally speaking BATFE frowns on open bolt semi-autos. You will not find any law that outright bans the production of all open-bolt designs. It's simply that no one has figured out a way to make a semi-auto open bolt gun that isn't (in BATFE's eyes) easily converted to full-auto. Theoretically, you could still build an open-bolt gun. In fact, I recall seeing I think SWD made an openbolt 12 gauge shotgun recently. Perfectly legal. Can't be converted....it's a single-shot.

There's probably some way you could make a semi-auto open bolt that BATFE would approve. The mechanism would just be too complex and costly to make.

Brian Pfleuger · May 7, 2013, 11:18 AM

Quote:

Originally Posted by Skans

The mechanism would just be too complex and costly to make.

Not to mention all the inherent downsides to accuracy. Folks spend money replacing springs, firing pins and whatnot to eliminate ignition delays measured in fractions of a millisecond. The time it takes for that bolt to close is a comparative eternity.

johnwilliamson062 · May 8, 2013, 12:17 PM

So a single shot can't easily converted to full auto and the ruling does not apply. moving forward with my design.

James K · May 8, 2013, 01:06 PM

To be a machinegun, a firearm has to fire more than one shot with a single pull of the trigger (or operation of the firing mechanism). A single shot with no magazine can't, by that definition, be a machinegun no matter how it operates.

Jim

444 · May 8, 2013, 02:07 PM

"Not to mention all the inherent downsides to accuracy. Folks spend money replacing springs, firing pins and whatnot to eliminate ignition delays measured in fractions of a millisecond. The time it takes for that bolt to close is a comparative eternity. "

This doesn't include the fact that any open bolt submachine gun I ever handled: the bolt is massive. It is by far the heaviest part of the whole gun. If you take the bolt out, all you have is a tube, short barrel, and the fire control components. So, when you have one of these guns on semi-auto, when you fire it, this massive bolt that weighs several pounds slams forward. I guess I am thinking of guns like the Sten, the Sterling, and things like that. On the Thompson, the whole thing is heavy and massive.

James K · May 8, 2013, 02:31 PM

Further, open bolt sub guns use advanced primer ignition to keep bolt weight down. When a sub gun is changed to a closed bolt blowback design, either the bolt has to be made more massive or the spring made a lot heavier. Since most closed bolt guns are built on sub gun receivers, increase of bolt mass may not be practical, and the extra spring tension makes initial operation more difficult.

Jim

manta49 · May 8, 2013, 02:41 PM

It depends what you are looking it for . If you are looking accuracy as said in other posts the open bolt design makes they difficult to shoot accurate on singles shot. That's one reason that the MP/5 is so popular it shoots from a closed bolt and is more accurate than open bolt designs.

Andy Griffith · May 8, 2013, 03:43 PM

Well, you could have an open bolt pump or lever action too.

Open bolt revolvers are just too complicated to make.

**Mike Irwin** · May 10, 2013, 08:09 AM

"Further, open bolt sub guns use advanced primer ignition to keep bolt weight down."

Or, you end up with guns like the Reising and the original Thompsons, which fired from an open bolt, but which had the odd and questionablely useful Blish lock.

I know there have been several other "open bolt, but locked at moment of firing" submachine guns over the years.

Gunplummer · May 10, 2013, 08:52 PM

I had a semi MAC 11 years back that fired with an open bolt. I KNOW that it is now illegal to manufacture these. I would check the laws, or better yet call the ATF and find out. Single shot? How hard is it to braze a magazine well to a tube?

James K · May 10, 2013, 09:40 PM

I once said that I could make a sub gun out of a barbeque grill and, given some basic tools, I think that is true. In fact the SMG is the easiest of all serious* guns to make, a lot easier than a handgun or a rifle. The hardest part to make from scratch would be the magazine.

*I don't count toys like "zip" guns or those "Philippine guerilla" shotguns.

Jim

May 6, 2013, 11:01 PM	#1
johnwilliamson062 Junior member Join Date: May 16, 2008 Posts: 9,995	All open bolts machine guns? I have been surfing the web looking at home made designs the last few days. I have seen a number of questionable designs. Maybe foreign made or maybe my eyes aren't accurate at measuring. One thing I have seen is single shots that fire from an open bolt. I was wondering if the prohibition on open bolts is limited to repeating arms, or if these items are illegal.

May 7, 2013, 08:56 AM	#4
cslinger Senior Member Join Date: July 14, 2002 Location: Nashville, TN Posts: 2,045	Yes, if it fires from an open bolt it is an easily convertible machine gun in the eyes of the ATF. Don't build or buy one unless you are licensed to build or it's a Pre 84 papered gun. __________________ "Is there anyway I can write my local gun store off on my taxes as dependents?"

May 7, 2013, 09:45 AM	#6
Mike Irwin Staff Join Date: April 13, 2000 Location: Northern Virginia Posts: 41,379	yep, firing from an open bolt is about as simple as it gets. Most often in such a design the "firing pin" is just a bump on the bolt face -- nothing mechanical about it. In effect, it's a slam-fire gun. There is something of an art to balancing the weight of the bolt, the power of the cartridge and the power of the main spring to make sure that the system is in balance and that the cartidges don't pop early, or not at all. __________________ "The gift which I am sending you is called a dog, and is in fact the most precious and valuable possession of mankind" -Theodorus Gaza Baby Jesus cries when the fat redneck doesn't have military-grade firepower.

May 7, 2013, 09:46 AM	#7
Mike Irwin Staff Join Date: April 13, 2000 Location: Northern Virginia Posts: 41,379	"I wonder how this could be true for a single shot with no provision for a magazine." I THINK Savage made such a rifle years and years ago. __________________ "The gift which I am sending you is called a dog, and is in fact the most precious and valuable possession of mankind" -Theodorus Gaza Baby Jesus cries when the fat redneck doesn't have military-grade firepower.

May 7, 2013, 10:59 AM	#8
Skans Senior Member Join Date: November 20, 2008 Posts: 11,132	Generally speaking BATFE frowns on open bolt semi-autos. You will not find any law that outright bans the production of all open-bolt designs. It's simply that no one has figured out a way to make a semi-auto open bolt gun that isn't (in BATFE's eyes) easily converted to full-auto. Theoretically, you could still build an open-bolt gun. In fact, I recall seeing I think SWD made an openbolt 12 gauge shotgun recently. Perfectly legal. Can't be converted....it's a single-shot. There's probably some way you could make a semi-auto open bolt that BATFE would approve. The mechanism would just be too complex and costly to make. Last edited by Skans; May 7, 2013 at 11:05 AM.

May 7, 2013, 08:15 AM	#2
Madcap_Magician Senior Member Join Date: August 13, 2009 Location: MN Posts: 668	Is there a prohibition on firearms firing from an open bolt? I am not aware of one. The only real reason to have a firearm fire from an open bolt is to aid cooling for moderate to rapid sustained automatic fire. I can't imagine what the point of a single-shot firing from an open bolt would be.

May 8, 2013, 12:17 PM	#10
johnwilliamson062 Junior member Join Date: May 16, 2008 Posts: 9,995	So a single shot can't easily converted to full auto and the ruling does not apply. moving forward with my design.

May 8, 2013, 01:06 PM	#11
James K Member In Memoriam Join Date: March 17, 1999 Posts: 24,383	To be a machinegun, a firearm has to fire more than one shot with a single pull of the trigger (or operation of the firing mechanism). A single shot with no magazine can't, by that definition, be a machinegun no matter how it operates. Jim

May 8, 2013, 02:07 PM	#12
444 Senior Member Join Date: November 20, 2000 Location: Ohio Posts: 3,968	"Not to mention all the inherent downsides to accuracy. Folks spend money replacing springs, firing pins and whatnot to eliminate ignition delays measured in fractions of a millisecond. The time it takes for that bolt to close is a comparative eternity. " This doesn't include the fact that any open bolt submachine gun I ever handled: the bolt is massive. It is by far the heaviest part of the whole gun. If you take the bolt out, all you have is a tube, short barrel, and the fire control components. So, when you have one of these guns on semi-auto, when you fire it, this massive bolt that weighs several pounds slams forward. I guess I am thinking of guns like the Sten, the Sterling, and things like that. On the Thompson, the whole thing is heavy and massive. __________________ You know the rest. In the books you have read How the British Regulars fired and fled, How the farmers gave them ball for ball, From behind each fence and farmyard wall, Chasing the redcoats down the lane, Then crossing the fields to emerge again Under the trees at the turn of the road, And only pausing to fire and load.

May 8, 2013, 02:31 PM	#13
James K Member In Memoriam Join Date: March 17, 1999 Posts: 24,383	Further, open bolt sub guns use advanced primer ignition to keep bolt weight down. When a sub gun is changed to a closed bolt blowback design, either the bolt has to be made more massive or the spring made a lot heavier. Since most closed bolt guns are built on sub gun receivers, increase of bolt mass may not be practical, and the extra spring tension makes initial operation more difficult. Jim

May 8, 2013, 02:41 PM	#14
manta49 Senior Member Join Date: July 15, 2011 Location: N Ireland. UK. Posts: 1,809	It depends what you are looking it for . If you are looking accuracy as said in other posts the open bolt design makes they difficult to shoot accurate on singles shot. That's one reason that the MP/5 is so popular it shoots from a closed bolt and is more accurate than open bolt designs.

May 8, 2013, 03:43 PM	#15
Andy Griffith Senior Member Join Date: May 14, 2009 Location: Macon Co. NC Posts: 591	Well, you could have an open bolt pump or lever action too. Open bolt revolvers are just too complicated to make. __________________ Barney Fife: "Nip it, nip it, nip it!" Andy Griffith:"Oh now Barn'...."

May 10, 2013, 08:09 AM	#16
Mike Irwin Staff Join Date: April 13, 2000 Location: Northern Virginia Posts: 41,379	"Further, open bolt sub guns use advanced primer ignition to keep bolt weight down." Or, you end up with guns like the Reising and the original Thompsons, which fired from an open bolt, but which had the odd and questionablely useful Blish lock. I know there have been several other "open bolt, but locked at moment of firing" submachine guns over the years. __________________ "The gift which I am sending you is called a dog, and is in fact the most precious and valuable possession of mankind" -Theodorus Gaza Baby Jesus cries when the fat redneck doesn't have military-grade firepower.

May 10, 2013, 08:52 PM	#17
Gunplummer Senior Member Join Date: March 11, 2010 Location: South East Pa. Posts: 3,364	I had a semi MAC 11 years back that fired with an open bolt. I KNOW that it is now illegal to manufacture these. I would check the laws, or better yet call the ATF and find out. Single shot? How hard is it to braze a magazine well to a tube?

May 10, 2013, 09:40 PM	#18
James K Member In Memoriam Join Date: March 17, 1999 Posts: 24,383	I once said that I could make a sub gun out of a barbeque grill and, given some basic tools, I think that is true. In fact the SMG is the easiest of all serious* guns to make, a lot easier than a handgun or a rifle. The hardest part to make from scratch would be the magazine. *I don't count toys like "zip" guns or those "Philippine guerilla" shotguns. Jim

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