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Thread: Mac jack

  1. #1
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    Mac jack

    I came across a cool looking device called the Mac jack but it appears itís
    Only for the M11? Is there one for the M10 and if not is there a reason why
    Something like this will not work with it?

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    The M11/NINE has some room behind the point at which the sear will catch the bolt. That extra room is where the Mac Jack is placed. There are a couple of ways to effect cyclic rate in an open bolt submachinegun, change the mass of the bolt or change the length of the stroke of the bolt. The Mac Jack shortened the length of the stroke to just beyond the point at which the sear can catch the bolt.

    The M10 stroke is pretty much at the point just beyond where the sear can catch the bolt. So the M10 doesn't have the extra stroke length that the M11/NINE has. So the M10 doesn't have the additional stroke length where a Mac Jack device would be placed. The stroke length of the M10 is why the TASK style conversion does make as much of an impact for the M10 as the M11/NINE. The M10 doesn't have the length of stroke the M11/NINE has. To increase the stroke of the M10 either the lower receiver would need to be lengthened, or the bolt would need to be shortened. The problem with shortening the bolt is the ejector would fall out of the bolt. I hope this answers your question.

    Scott

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    Good to know, learned something new today thank you both!

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    Awesome! Thank you for the response Scott.

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    What the M10 lacks in stroke, it makes up for in girth.
    Last edited by Gaujo; 04-05-2021 at 11:31 AM.

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    Quote Originally Posted by Gaujo View Post
    What the M10 lacks in stroke, it makes up for in girth.
    Yes and no in my opinion. Certainly the M10 factory 9mm bolt has more mass than the M11/NINE factory bolt. So in factory configuration the M10 9mm is the slowest cyclic rate. The whole point of the TASK system is to add mass to the bolt to slow the cyclic rate. I am fortunate enough to have a TASK modified M11/NINE and M10 receivers. Because of the additional stroke, the M11/NINE is much easier to slow to pull singles. With the M10, I have added so much mass that the gun would short stroke. Icutbackjustoneounce. I still found it difficult to pull singles. It was too easy to pull the trigger far enough to release the bolt. But I could not let go of the trigger quickly enough to catch the bolt, so I get doubles. It was suggested to me to add a screw to the trigger to limit over travel. Since I am using my M10s with Tenko testing, I really don't want to limit trigger travel.

    Something that I have in the back of my mind is to cut down one of my spare TASK modified bolts and cut it close to the spring in the extractor. Then drill out the hole for the ejector to have a sleeve the would support the ejector. I would make the sleeve spring loaded so that the sleeve would collapse inside the bolt when the bolt goes to the back of the receiver. Maybe the extra throw will help me to pull singles easier.

    Scott

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    gaujo, i see what you did there.

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    does anybody sell Mac Jacks or have dimensions to make myself?
    thanks

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    Ok, not to totally change the subject, but for the Open Bolt UZI SMG, you can accomplish the same thing with a UZI Semi buffer. Cut a piece about 1/2 inch long. I feel this provides a little more than factory RPM and is very nice rate. Plus you have a longer piece left over, if you want to raise the rate even more.

  10. #10
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    Quote Originally Posted by gomelkiev View Post
    does anybody sell Mac Jacks or have dimensions to make myself?
    thanks
    Tactical Innovations sells them but they are out right now. I would think that you could easily make one with a block of Delrin or similar material, or even some tough wood for that matter (won't last as long but it's made from scrap).

    For the M10 I wonder if one put a larger diameter and much shorter and stiffer spring over the main spring if that could act in a similar fashion. Of course the spring would need to be wound in the other direction so that the coils don't interlock and bind. Might be worth a look through my spring collection for a test victim.

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    From photos it's hard to see if mac jack just whole piece of delrin or it has some holes or specific profile. I ordered speed cube from usmachinegun and also planning to get block of delrin.

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    Quote Originally Posted by skoda View Post
    For the M10 I wonder if one put a larger diameter and much shorter and stiffer spring over the main spring if that could act in a similar fashion. Of course the spring would need to be wound in the other direction so that the coils don't interlock and bind. Might be worth a look through my spring collection for a test victim.
    Any firearm has a balance in the bolt group. The bolt group needs enough energy for reliable function. Too much energy and the bolt beats on the back of the receiver. Too little energy in the bolt group, the gun short strokes and malfunctions. I don't know if there is enough room in the spring channel in the bolt to add an additional spring around the outside of the recoil spring. You could add more spring to what is already there. You have to be careful as to how much you add. If the spring has no room between the coils fully compressed, the bolt will crush the spring and destroy it.

    The most you could do would be to make the spring strong enough to have the bolt just touch the buffer. The sear catch point of the M10 is pretty close to the end of the bolt stroke. If the bolt doesn't have enough energy to overcome the spring to get to the sear catch point, the gun will run away. Much less than that, the bolt won't go far enough back to grab the next round in the mag and short stroke. That is why the M11/NINE works so much better at being sped up or slowed down as there is much more stroke behind the sear catch point than the M10. Good luck with the project.

    Scott

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    Always so much real great useful knowledge from Scott, thank you Sir.

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    Of course Scott. It would have to be something fairly short and very stiff to do much. I was thinking of an automotive valve spring cut down to somewhere around half an inch, maybe a bit more.

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    Certainly you can try that. I would start out with four or five rounds in the mag, just incase the bolt can't overcome the added spring and the gun runs away. I don't remember the numbers but as I recall, the M11/NINE bolt is lighter than the M10/9 bolt. That is why even with the longer stroke of the M11/NINE, it still has the higher ROF. So I would imagine that the M10/9 bolt could be lightened to the mass of the M11/NINE bolt. I would recommend caution. The mass of the bolt and the recoil spring pressure keeps the chamber closed during the high pressure phase.

    At a machinegun shoot I remember an M16 registered receiver owner had an OOB detonation. He was using a Colt style 9mm conversion. He was unaware that the conversion required a heavy buffer. Luckily for him when the base of the shell ruptured, the scars of brass sprayed the inside of his receiver, instead of spraying out the port door. When we looked at the brass of the rounds he had just fired, all of it was bulged. He was using an H buffer, which is 3.8 oz. The Colt 9mm buffer is 5.5 oz. Apparently the H buffer was not heavy enough to keep the shell inside the support of the chamber, and a shell ruptured. So I would think that the bolt could be lightened to the mass of a M11/NINE bolt. I don't know if I would go any lighter than that. The lightened bolt could be used with a stronger spring.

    Me, I would rather slow the cyclic rate than speed it up. If more mass could be added to the M10 bolt, then a lighter spring could be used. It would be extra cool if the M10 bolt could be shortened to the stroke of the M11/NINE, but had more mass, that would be even better. That would be a project that I would be interested in.

    Scott

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    Quote Originally Posted by Gaujo View Post
    What the M10 lacks in stroke, it makes up for in girth.
    Lol

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    Mac Jack and Speed Cube are virtually identical.

    Theyíre both a solid cube of plastic that makes the bolt have less travel thereby speeding up rate of fire. Physics.

    Iíve posted this vid once before. Itís a stock-style M11/9 with a speedcube/macjack 50 rounds.


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    Yep...Its like a 1" x 1" x 1" chunk of delrin or whatever with a couple holes / slots drilled through it.

    Nothing fancy at all.......https://www.tacticalinc.com/image/pr...ack-1-500.jpg?


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    Can the Mac 11 380 be sped up, if the Mac 11 9 can reach speeds of the Mac 380 or even more iv heard can the Mac 380 be speed up wich is truly the fastest or can be made faster thnx

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    Quote Originally Posted by Macdaddy69 View Post
    Can the Mac 11 380 be sped up, if the Mac 11 9 can reach speeds of the Mac 380 or even more iv heard can the Mac 380 be speed up wich is truly the fastest or can be made faster thnx
    The Lage 9mm Speed Bolt for the A1 is a thing of high-ROF beauty.

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