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Thread: Tube gun from scratch

  1. #41
    CNCer & gunco junky jonmorry333's Avatar
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    Quote Originally Posted by muttman View Post
    no no no, do not make a 12 ga blow back. you wount like the what happens.
    muttman
    why ??? it has to much blow back ??? but couldn't i use a smaller port hole diameter and vent the gas tube . i was thinking about using the aks spring too
    VERITAS AEQUITAS

  2. #42
    gunco irregular moleman's Avatar
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    Quote Originally Posted by jonmorry333 View Post
    why ??? it has to much blow back ??? but couldn't i use a smaller port hole diameter and vent the gas tube . i was thinking about using the aks spring too
    If its going to be blow back then why are putting a gas port hole and tube on it? what are you driving with the gas system? About the only way a straight blow back 12 ga would work is an extremely heavy bolt and spring. Another option that might work is a delayed blowback, make your piston large and the gas pressed on the back side of it to drive it forward for a sort of delayed blowback. I don't even know if either of those two things would be feasable or REMOTELY SAFE. Take a look at a remington 1100/870 shotgun. The flapping locking lug should be adaptable to a tube type receiver and would much safer.

  3. #43
    GuncoHolic kernelkrink's Avatar
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    Look up the Atchisson shotgun, it morphed into the current gas operated AA12 model.

    Modern Firearms - Atchisson assault shotgun / AA-12

    The blowback model had a 3lb+ bolt.

  4. #44
    gunco irregular moleman's Avatar
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    Wow thats neat Kernel, and a lot lighter bolt at 3bls than what I would of thought. Would a semi bolt have to be heavier since we couldn't use the open bolt with advanced ignition?

  5. #45
    GuncoHolic kernelkrink's Avatar
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    Probably. Someone with a fancy calculater would have to do the math to get it right the first time, but shotgun shells are relatively low pressure rounds compared to say a centerfire rifle. SAAMI specs most shells around 11,000 psi up to 14,000psi for a magnum. That's low. The .308 specs at 62,000 and IIRC HK says the G3 bolt would have to be around 32lbs to work properly without the roller delay mechanism. Square inches of cartridgehead pressing against the bolt would factor in as well, 11,000 psi on a one inch head would equal 14,000 lbs pressing against it, a 2 inch one would double that to 22,000 lbs. Somewhere in there is the right answer!

    SAAMI pressures

  6. #46
    Gunco Veteran Viper Dude's Avatar
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    Hello All,
    The Atchisson blowback 12 guage bolt was about twice the mass of the usual Sten 1.4 lb 9mm smg bolt.

    Recall however that the WW-II "Philipine guerilla gun" simply used a slidiing 12 guage barrel (ie pipe) inside another steel tube (ie pipe) to manually smash the chambered round against a fixed firing pin. No lock was used - breaching by "armstrong". haha.

    After WW-II this simple shotgun was produced commercially by its' inventor (the original "American Guerilla in the Phillipines" not Tyrone Powers).

    Also recall that the pre-WW-I von Manlicher 1894 auto pistol used a simple "blow-forward" barrel and a fixed breach to operate as did the Schwarzlose M-08 pistol. Perhaps in this ancient technology is a solution to the idiot-simple semi-auto shotgun, carbine, pistol, etc.

    VD

  7. #47
    Gunco Veteran muttman's Avatar
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    Quote Originally Posted by jonmorry333 View Post
    why ??? it has to much blow back ??? but couldn't i use a smaller port hole diameter and vent the gas tube . i was thinking about using the aks spring too
    #1 recoil
    #2 saftey
    #3 the fed's

    #1 can be delt with but 2 and 3 are not too fun to deal with.
    if you read the link that kernel posted the desinger changed the gun to lock breach for saftey. muttman

  8. #48
    Gunco Veteran perry's Avatar
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    has anybody seen the 12 ga. machine gun? belt feed and built like a ma2.

  9. #49
    Gunco Veteran perry's Avatar
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    i think it was on youtube.

  10. #50
    Gunco Member jlwilliams's Avatar
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    Maybe a little bit of a curve ball, but why not design a gun that uses an existing pistol cal bolt? Why not make it use a Cobray bolt? They are a hammer struck design, so you could probably use the AR trigger group for it. It would have to be a square tube gun, but it would still be a tube gun. Then, after you have done the drafting project, you could buy some steel tubing and make the gun.

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