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Thread: Tube gun from scratch

  1. #11
    Gunco Member deth502's Avatar
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    Quote Originally Posted by BHP View Post
    As a type 07/02 I have been planning an open bolt 10mm with some features of the CZ26 and a layout similar to the Beretta PM 12. If it works I had planned to build a semi variant but I haven't gotten into the semi design phase yet. FA first, SA somewhere after that.
    actually, yes, he can build an open bolt.

    but you are correct in that most people cant.

  2. #12
    Gunco Member couch commando's Avatar
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    I love tube guns, hugh fun factor.

  3. #13
    Gunco Rookie puddle pirate's Avatar
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    Well I decided to design for my CAD class project and portfolio material a 9mm machine pistol. My instructor agreed to my doing this but I have to flip it to a semi auto only design. It's originally designed as a square tube reciever w/ a piece of high pressure hydraulic tubing for the barrel. I'm gonna flip it to a tube reciever, semi auto, closed bolt, floating firing pin, AR style ejector pin, and either design my own disconnector in conjunction with the supplied trigger group design or use a AR style trigger group, and a AK style guide rod w/ spring. And of course a rifled barrel. I have to make it pretty for him. So I'm thinking ventalated barrel shroud, custom pistol grip of some kind, and G3 style sights. And he wants me to show the various springs compressing and de-compressing in Inventor. All drawings will be in both AutoCAD '09 and Inventor '09. So wish me luck.

  4. #14
    gunco irregular moleman's Avatar
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    Quote Originally Posted by puddle pirate View Post
    Well I decided to design for my CAD class project and portfolio material a 9mm machine pistol. My instructor agreed to my doing this but I have to flip it to a semi auto only design. It's originally designed as a square tube reciever w/ a piece of high pressure hydraulic tubing for the barrel. I'm gonna flip it to a tube reciever, semi auto, closed bolt, floating firing pin, AR style ejector pin, and either design my own disconnector in conjunction with the supplied trigger group design or use a AR style trigger group, and a AK style guide rod w/ spring. And of course a rifled barrel. I have to make it pretty for him. So I'm thinking ventalated barrel shroud, custom pistol grip of some kind, and G3 style sights. And he wants me to show the various springs compressing and de-compressing in Inventor. All drawings will be in both AutoCAD '09 and Inventor '09. So wish me luck.
    You may want to rethink the ar15 type ejector plunger setup. In order for that to work you'll need to have a feed lip which is a smg feature according to the atf. Now I know there are approved semi designs out there with feed lips, but most of the approval letters you see for tube guns state you have to remove the feed lips to keep you from being able to jam the firing pin forward for an instand smg.

  5. #15
    Gunco Rookie puddle pirate's Avatar
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    ok now my ignorance is gonna show. please expound on the feed lip issue as I do not know what your refering to. I took the idea for the ejector from the AR bolt as the original design did not have one.

  6. #16
    gunco irregular moleman's Avatar
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    Quote Originally Posted by puddle pirate View Post
    ok now my ignorance is gonna show. please expound on the feed lip issue as I do not know what your refering to. I took the idea for the ejector from the AR bolt as the original design did not have one.
    The feed lip is the bottem of the recessed area on the bolt face that incloses the case head. Here is a picture of two suomi bolts. The one on the left has not been modified to semi yet and has the feed lip area colored in blue. The one on the right has been turned down to a smaller diameter to prevent an unmodified bolt being used in the same gun. It also has been drilled out for an AR15 firing pin and has had the feed lip area removed. I hope this helps. If you're just drafting a design it doesn't really matter, but if you're going to make one it would be best to show the design to the atf tech branch as they are the ones that are going to make up the standards on which it is classified by.
    Attached Images Attached Images

  7. #17
    Gunco Rookie puddle pirate's Avatar
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    First off I would like to just say thanks for taking the time to explain this to me. I do greatly appreciate it. This why I posted it here becuase I knew if there was any mistakes or booboo's someone would point them out quickly. I 'm really pretty good on most of these things concerning the laws however that particular item is new to me. Now to try this again as my post was denied /deleted becuase it seems Gunco forgot I was logged in.

    Ok one more time. So if by making a custom/one off closed bolt semi auto pistol w/ a floating firing pin I have to grind flat the bottom of the bolt where the feed lip is so this will somehow prevent the floating firing pin from somehow jamming in the fwd position and thus allowing the gun to go full auto? All becuase I chose to design/build a tube gun? All I can say is wow............. Sorry for my sarcasm, I'm just amazed is all.

    So would this also apply to a square tube reciever as this was the original design of the weapon. If not I'll go back to the original design and go from there. And again thanks for taking the time to explain this to me.
    Carl

  8. #18
    Gunco Rookie puddle pirate's Avatar
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    And also the reason this matters is I did promise my instructor to make sure as best I could that the design would be in compliance with applicable state and federal laws. So this why I keep asking questions.

  9. #19
    gunco irregular moleman's Avatar
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    No one has ever accused the atf of being fair or consistant.

  10. #20
    GuncoHolic kernelkrink's Avatar
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    On a full auto open bolt gun, the firing pin is sticking out of the breechface. This is how they work, as the round is chambered the cartridge bottoms out in the chamber and the bolt continues forward, slamming the pin into the primer and firing it. The breechface of the bolt has to be recessed for this to work, otherwise the cartridge would slide up under the extended firing pin and jam against it instead of riding in front of it. By removing the bottom part of the bolt and making the breechface essentially flat where the cartridge is fed from the mag you prevent the possibility of someone jamming the pin forward and letting it go full auto as the cartridge will slide up under the pin and jam against it. The M11 nine series of semi autos, for example, still has this fully recessed breechface on their bolts even though they are semi auto. If the firing pin were to get jammed in the forward position you would have a runaway full auto as there is no way to stop the bolt cycling other than a jam or running out of ammo. A safety issue as well as a legal one.

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