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Thread: Gas operated wonder 9?

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    gunco irregular moleman's Avatar
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    Default Gas operated wonder 9?

    I've been taling about building a 9mm direct impingement upper since this past april and have been gathering parts since early summer. Over the past two weeks I've managed to make some progress on the build.
    I started with: a 9mm blank; a $10 barrel extension from CDNN; a spare carrier and upper I've had for years; A set of used USGI bolts off of gunbroker; and a Caterpilliar diesel engine nut 13/16"-16tpi.
    The barrel blank I started with was one of the .800" blanks that have been floating around for the past few years. This barrel is too thin to turn a shoulder into for the barrel extension to rest against. I decided to used a savage style locknut to solve this problem. An internet search turned up Catapilliar diesel engine grade 8 nuts for about $1.50 each so I got several.
    After short chambering the barrel I threaded the last 1.150" of the barrel to 13/16"-16tpi so that the barrel extension was a little difficult to thread on. Then I screwed on the barrel extension so that the back end of it was 1/2" from the back end of the barrel and drilled the index pin hole to a depth of just past the bottem of the barrel threads. I also drilled a gas port about 1.5" in front of the barrel extension since it was already squared up. Then I screwed on the locknut as far as it'd go, and then screwed on the barrel extension with red locktite and secured it with the index pin made from 1/8" drill rod. After letting it set for a day I torqued down the lock nut and secured it with red locktite. Before the loctite set up I turned down the locknut to just under 1" with the barrel extension towards the tail stock so that any cutting force would be tightening the lock nut and not loosening it. Then I finished chambering the barrel after opening up the 556 bolt to .398" so the 9mm case would fit.
    I then made a gas block for it out of steel and cut down a used rifle length gas tube to fit. The first few rounds of test fire showed that with a .090" gas port the bolt comes back enough to extract the case from the chamber and stop with the hammer half cocked so that the hammer catches the firing pin as it tries to go forward.
    Thats where I'm at right now. The wonder 9 part of it is I wonder what it'll take to get it to run. More work and current photos to come!
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    Last edited by moleman; 12-26-2010 at 02:20 PM.

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    Gunco Member wrench1957's Avatar
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    Very cool, and ingenious. I will be following this thread as I like to see creativity like this. Will you use ar15 9mm mags or some other?
    Also off the top of your head do you think this would be possible with .45 ACP?
    Do it before it is too late!
    Proud member of the NRA,GOA and JPFO!!!
    And now GOCRA in MN!!!!

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    gunco irregular moleman's Avatar
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    Quote Originally Posted by wrench1957 View Post
    Very cool, and ingenious. I will be following this thread as I like to see creativity like this. Will you use ar15 9mm mags or some other?
    Also off the top of your head do you think this would be possible with .45 ACP?
    I had been talking it over with several members and would like to thank Viper Dude and Mad Machinest for their input. I would like to see if I can get pps43 mags to work, and use that same mag for 9mm, 762x25, and 45acp. Mad Machinest currently sells 762x25 and 45acp uppers so I would defer all questions about those to him. Once I get the bolt carrier to cock the hammer I'm going to use a modified sten mag for the mean time. I tried several carriers, Colt, FN, and unknown in both ar15 and M16 styles. The one that shows the most promise is a very well worn converted colt m16 carrier. It is pushing the hammer down enough to get caught on the firing pin collar (its a semi converted carrier) so it just needs a little more to lock the hammer on the disconnector. If it turns out it doesn't work, I can always cut the barrel off at the gas port and make a 16" blow back out of it.
    Last edited by moleman; 12-26-2010 at 09:20 AM.

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    Gunco Member wrench1957's Avatar
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    I know that you are working with gas operation but if you did go to blowback how would you balance the recoil impulse, with heavier recoil spring or heavier bolt weight, or both?
    Is there a formula for that or is it trial and error?
    Do it before it is too late!
    Proud member of the NRA,GOA and JPFO!!!
    And now GOCRA in MN!!!!

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    Gunco Member wrench1957's Avatar
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    I know this might be a little personal but could you show us pics of your gas block?
    Do it before it is too late!
    Proud member of the NRA,GOA and JPFO!!!
    And now GOCRA in MN!!!!

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    Gunco Veteran Bolt2bounce's Avatar
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    If your using a standard AR-15-M-16 carrier?? you may want to lighten up the carrier a bit, the 9mm cartridge will only produce so much gas it may need more than it can produce with the 9mm powder burn.. You can ope up your gas port hole, and or move gas port location closer to the chamber.. location of the gas hole also will effect the cycling.. I think you can get it to work, but it's gonna be ammo sensitive... B2B

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    gunco irregular moleman's Avatar
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    Wrench, if I end up going the blowback route (which I don't think I'll have to) I'll make my bolt the same weight as a colt or rra 9mm bolt and use a heavy 9mm buffer. I'll get some more pic's up later today of the gas block ect. I haven't profiled the gas block yet to fit under the handguard so it's pretty much like the block of steel above the barrel in the photos.
    B2B, It's still a work in progress. The gas block I made is a set screw type for easy removal to open up the gas port and so that I can move it back as needed. The 1.5" location and .090" gas port were just best guesses and are subject to change as I debug the thing. I'm trying to get it to work with a standard carrier and buffer first, and If I can't I'll lighten those up as needed. Ammo sensitivity isn't an issue for me since I reload just about all the pistol ammo I shoot.

    Edit: Here's a pic of the gas block so far. It really is a "block" at this point, but I'm going to mill away where the black sharpie marker is so that it'll fit under a set of standard handguards and to lighten it some.
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    Last edited by moleman; 12-26-2010 at 11:12 AM. Reason: add pic

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    Gunco Veteran [486]'s Avatar
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    Quote Originally Posted by wrench1957 View Post
    I know that you are working with gas operation but if you did go to blowback how would you balance the recoil impulse, with heavier recoil spring or heavier bolt weight, or both?
    Is there a formula for that or is it trial and error?
    What I would do is calculate the energy the bullet has, and then that is the same energy that the bolt has to absorb. The .45 is a straight walled case, so the pressure acting on the base of the bullet is the same as the pressure acting on the bolt face. Calculate the energy that is imparted on the bullet and you can figure out a good bolt weight.

    230 grains times 830 FPS = 190,900 divided by 20FPS [a high end of reasonable bolt speed] = 9545 grains

    Your bolt/buffer combo should be at least 9545 grains, which happens to be 1.36 lbs. I'd try and go heavier than that by a little, as it seems a bit light to me, but my calculations up there didn't take into account the force of cocking the hammer and what little force the recoil spring puts into it holding the bolt in battery.

    Who said we'd never use this stuff ever again in math class?

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    Gunco Member wrench1957's Avatar
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    Hey Moleman,
    Could you put an adjustment screw on the gasblock to adjust the amount of gas allowed through the block? Kind of like a mixture screw on a carburetor. You would open up the gas port hole in the barrel and rely on the screw to throttle it back a bit. Then adjust it to your particular load of the day.
    Do it before it is too late!
    Proud member of the NRA,GOA and JPFO!!!
    And now GOCRA in MN!!!!

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    gunco irregular moleman's Avatar
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    Wrench, Yep I have thought about tapping the block for a modifed ss set screw to do just that. That is part of the reason the gas block hasn't been profiled yet. It's gonna be a lot easier to lay out the hole locations with everything flat and square. I did manage to tweek it a bit an now it is ejecting and cocking the hammer!!! Now I need to finish modifing the sten mag to work.
    Last edited by moleman; 12-26-2010 at 04:56 PM.

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