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Thread: 12 ga upper for M-11/9 project

  1. #41
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    I don't claim to be an expert in ATF opinions, but;
    maybe if you deliberately designed the conversion to require multiple parts, such as
    1) an "extension" that attaches to the MAC Lower that holds the Mag, Bolt, Springs, etc,
    2) a seperate Upper that holds the Barrel,
    You might get it approved because
    1) The "Extension" will be unusable without both the MAC lower AND the "Upper";
    2) The "Upper would be unusable without the MAC Lower AND the "Extension.

    Just a thought.

  2. #42
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    The lack of consistent logic ensures no one is an expert in ATF opinions! Again- not looking for design "approval" to manufacture but looking to comply with the law also. This is all good info- as usual! I'm going to think it over- have some drilling and welding to do this weekend, before I can kick this one off.
    Last edited by rybread; 06-09-2017 at 03:30 PM.

  3. #43
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    I don't care how it's made or what mags or belts it takes. Just put me on the list.

  4. #44
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    Trying to think outside the box here. Would it be possible to build an upper working off of a long recoil design such as the Browning A5? Using the barrel and tube magazine with the friction recoil spring setup on the magazine tube. With a sear catch to capture the bolt in the open position after the barrel returns into battery. The bolt return spring would still be using the rear plate on the Mac receiver. Firing pin would be pinned or welded to become fixed firing pin like other open bolts. Bolt would be fairly light so it would take a lot of stress off of the receiver, but not sure if you could get enough energy on a light bolt to chamber and fire a round. Also upper receiver may require more machining than can be done in a home shop.

  5. #45
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    Quote Originally Posted by nklf View Post
    Trying to think outside the box here. Would it be possible to build an upper working off of a long recoil design such as the Browning A5? Using the barrel and tube magazine with the friction recoil spring setup on the magazine tube. With a sear catch to capture the bolt in the open position after the barrel returns into battery. The bolt return spring would still be using the rear plate on the Mac receiver. Firing pin would be pinned or welded to become fixed firing pin like other open bolts. Bolt would be fairly light so it would take a lot of stress off of the receiver, but not sure if you could get enough energy on a light bolt to chamber and fire a round. Also upper receiver may require more machining than can be done in a home shop.
    Man that is outside the box, but unnecessarily complex. This can be done with far less effort than that would require! It's a realatively simple mechanical device..

  6. #46
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    After some consideration I have a plan. given my limited capabilities I considered a few options and decided on one that I think is within the law (comparable to other available uppers) and requires the fewest engineering feats to be accomplished. In fact my design is relatively simple and should not require extreme precision. I woke up Tuesday with an idea for a part that would allow the Mac bolt to act as a hammer, being released only when the 12 ga bolt slams home and the trigger is pulled. This solves or entirely avoides several potential issues. Of all the options I've looked at this one seems to be the best.. it feels right! More to come..

  7. #47
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    Quote Originally Posted by rybread View Post
    After some consideration I have a plan. given my limited capabilities I considered a few options and decided on one that I think is within the law (comparable to other available uppers) and requires the fewest engineering feats to be accomplished. In fact my design is relatively simple and should not require extreme precision. I woke up Tuesday with an idea for a part that would allow the Mac bolt to act as a hammer, being released only when the 12 ga bolt slams home and the trigger is pulled. This solves or entirely avoides several potential issues. Of all the options I've looked at this one seems to be the best.. it feels right! More to come..
    Interesting!

  8. #48
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    If you use the MAC Bolt as your "striker", you will possibly run into problems with feeding and ejection, because the length of (MAC) Bolt travel may not be sufficient for shotgun shells. I don't know the distance it travels, but a shotgun shell is quite a bit longer than a pistol cartridge.

  9. #49
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    Quote Originally Posted by sniperdoc View Post
    If you use the MAC Bolt as your "striker", you will possibly run into problems with feeding and ejection, because the length of (MAC) Bolt travel may not be sufficient for shotgun shells. I don't know the distance it travels, but a shotgun shell is quite a bit longer than a pistol cartridge.
    Extended bolt in a custom "upper" channel- hopefully this weekend I can take measurements and start prototyping parts. *modified bolt is more accurate. But good thinking Snipe- accommodating the longer bolt travel is just about the hardest part of making this work!

    Also, to prevent this beast from appearing to be novelty length, it may look more like an M240 than a 1919 (except with the gas tube on top vs. bottom).
    Last edited by rybread; 06-16-2017 at 04:57 PM.

  10. #50
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    Mmmmm yeah- I'm going to make it look like this...


  11. #51
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    Re: OAL; If you use a Side (like STEN) or Top (like BREN) mounted Mag, you won't have to worry about the bottom of the lower.

  12. #52
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    No worries. Going to keep it down low for a few reasons- mostly for drum mag usage. Not going to complicate it any more than needed. This is going to be a long journey as is. The m240 size and shape is really ideal for this.

  13. #53
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    A drum mag will definitely need to be bottom mounted.
    Side mounting one would make the gun extremely unbalanced, and top mounting a standard drum would block all possible sight options except lasers. With a stick mag, you could offset sights,but I don't see how you could with a drum.
    OTOH, a "Pancake" drum would be awesome!

    However, using a top mounted drum setup isn't terribly complex, essentially you turn the feeding mechanism upside down. But I do understand the wisdom of keeping it simple and following an existing pattern.

  14. #54
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    I have considered that- side fed, to accommodate a chute and send spent brass downwards or top fed so the gas tube would be on the bottom but I think from a design standpoint it's best as is. I'm about 80% there on design which may not sound like much or make for good videos but I'm excited- this could really work!

  15. #55
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    Ok safe to say design is at 100% now. The real beauty of this thing is the 1919 type assembly. I'm using a modified bolt & Mac upper and they're going to be sandwiched between two steel plates, with the Saiga bolt, trunnion & barrel- the modified bolt using a channel in the top cover or plate to ride in. Not intentional but as I worked through how to make it work, the 1919 type approach came to be the best solution. The Duke will be pleased, and I think there is real potential to use this approach for other caliber options. I'll be drafting up the bolt dimensions this week. My forecast is 12-18 months- basically make one part, verify or modify the set up then make the next part etc. until done. Slightly easier than the MG-43 since the parts are new vs. modifying existing ones.

  16. #56
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    Drafting done, will submit the bolt design to my shop tomorrow. Imagine a standard Mac upper with the front block off, leaving the receiver pin block below the path of the bolt.. basically like a Lage upper with an open front/ no barrel trunnion. This gets bolted between 2 steel plates via steel blocks welded to the upper.. Now you have a 1919 style upper into which you can put a larger bolt, a barrel and magwell. The top has a channel and the sides have rails to guide the bolt.. opens up lots of ammo choices. If the 12ga works, I'll move onto .50 or something that will penetrate small books

  17. #57
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    Slow moving here but maintaining forward progress. After reviewing an ATF approval letter shared on a recent thread I've scrapped the Saiga parts to strictly construct the upper from "all new parts/ no pre-existing firearm receivers" (since the Saiga trunnion was serialized). This means 12 ga barrel blank. M240 top cover, carry handle & butt stock. This means open bolt, and a heavy one.. but as always all changes are for the better.. this removes any potential lawful ambiguity while also improving/ simplifying the design which is always better!

  18. #58
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    I think the early work of Max Atchisson would be a good starting point for an 12 ga M11 upper.
    http://www.smallarmsreview.com/displ...idarticles=409
    The 380 MAC is the best caliber or they would not have put on the cover of THE MAC MAN. ;)

  19. #59
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    Thanks, good read- I am familiar with his work. A primitive but nice variant of the AA12 there!

  20. #60
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    Just curious with the 5.56 upper and the 12 gauge. Wouldn't there be a fear of stress on the receiver pin holes? I feel like the upper/lower set up puts more pressure on the pins than an M16 or shotgun. Then again I have no engineering background.

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