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Thread: .25 cal Disco Pumper Carbine

  1. #1
    Moderator rsterne's Avatar
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    .25 cal Disco Pumper Carbine

    I started work on the internal parts for my .25 cal Disco Pumper today.... It will use the MRod barrel and Disco breech I mated up the other day, plus an extended Disco valve with a check valve built in just ahead of the gauge port.... The valve extension will include a gauge mount for a 1500 psi gauge.... Here is the piston and the front mounting block to fit a Benjamin 392 linkage into the Disco....



    There will be a barrel band mounted on the stub of the front block which projects 3/8" ahead of the shortened Disco tube.... The barrel band will be 1/8" behind the muzzle of the MRod barrel....



    The next step is to cut the Disco tube to length, and machine an 8" slot in the bottom for the linkage.... and drill the hole for the front pivot pin....

    Bob
    Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
    Airsonal: Too many to count!

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    If this works out great you will have to make plans and let us copy them for free,
    can't wait to see your results.
    Benjamin Discovery Mac1 modded <----- Ya Baby the new toy
    Webly Alecto .177
    QB79- with lots and lots of mods HPA <------ Go too AirGun for FT

  3. #3
    Moderator rsterne's Avatar
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    With all due respect, Frank, perhaps you should keep notes.... When I want plans I often just add dimensions to a photo.... Detailed drawings are important when you need to reproduce something.... Since virtually all of my projects are "one-off" designed for my own entertainment, and not to make money.... why would I take the time to make detailed drawings and then "give them away".... Sounds like a government "make-work" project.... except they get paid for it....

    Once again, here is how it works, for me.... I do my own thing.... I don't make parts or guns for anyone else.... I try and document what I do and share it with others, and I do that free of charge.... Beyond that, you are welcome to borrow any ideas you see, and make any parts that are copies of mine.... but I think it's a bit much to ask me to do drawings as well....

    Bob
    Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
    Airsonal: Too many to count!

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    well I love your idea it's thinking out side the box and if it works great I'm going to copy your palns if you let me and guide me to build mine.
    Benjamin Discovery Mac1 modded <----- Ya Baby the new toy
    Webly Alecto .177
    QB79- with lots and lots of mods HPA <------ Go too AirGun for FT

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    Nice to see you are on to another project.
    I liked what you did with your uber pumper and you shared all your ideas with everyone.
    I will be following this project too and suggest that Frank print off all the info you post.

  6. #6
    Moderator rsterne's Avatar
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    I machined the Disco tube today.... cut it to length and squared the end and then machined the slot for the pump linkage....



    The tube is 1/2" behind the front of the MRod barrel, and the 3/8" barrel band will fit over the stub of the aluminum front plug.... leaving the front of the barrel band 1/8" behind the muzzle.... The pivot pin is 5/8" behind the front of the tube, and the slot is 8.2" long.... The stroke is 7.6" and the piston is 6.7" from the link pin to the compression face.... That leaves the compression face 0.3" ahead of the front of the gauge hole, which leaves room for the O-ring to seal the valve....

    The next step will be to make the extended front end for the valve incorporating the gauge mount and check valve.... Incidently, the front of the Disco stock comes to just behind where the spring sticks through the lever (the bump in the photo).... It will be cut just in front of the gauge, with the forestock becoming the pump handle.... Should work perfectly....

    Bob
    Last edited by rsterne; Oct 16 2012 at 06:48 PM.
    Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
    Airsonal: Too many to count!

  7. #7
    Member jgoodz420's Avatar
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    Looking good Bob

    This thing should be a beast can't wait to see the numbers you get out of it...
    "Just because you can, doesn't mean you should..."

  8. #8
    Moderator rsterne's Avatar
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    The swept volume is 54 cc.... My Uber-Pumpers with the 2100/2200 tube are 24 cc.... so over twice the volume per pump.... over 3 times what a 13XX pump moves.... The down side is that at 1500 psi the load on the piston is 650 lbs. instead of 450 lbs.... I am not aware of anyone using a metal Flat-Top Piston with a 392 linkage before.... The 392 valve can't be machined flat without exposing the check valve, so they just shim the pump cup to reduce headspace.... There is a lot of new territory being explored here.... or at least if it's been done before it is not documented (that I can find).... If the linkage buckles, I'll get a billet linkage from Mac1 Airguns.... I already have one of their exteneded ones, with a 3" longer lever, for the followup rifle version with internal reservoir for retained air (ie PCP with onboard pump).... and I just got the tube and valve from Eric today.... Pretty funny, haven't even finished this one, and I already have plans for the next one....

    Bob
    Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
    Airsonal: Too many to count!

  9. #9
    Member jgoodz420's Avatar
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    Quote Originally Posted by rsterne View Post
    The swept volume is 54 cc.... My Uber-Pumpers with the 2100/2200 tube are 24 cc.... so over twice the volume per pump.... over 3 times what a 13XX pump moves.... The down side is that at 1500 psi the load on the piston is 650 lbs. instead of 450 lbs.... I am not aware of anyone using a metal Flat-Top Piston with a 392 linkage before.... The 392 valve can't be machined flat without exposing the check valve, so they just shim the pump cup to reduce headspace.... There is a lot of new territory being explored here.... or at least if it's been done before it is not documented (that I can find).... If the linkage buckles, I'll get a billet linkage from Mac1 Airguns.... I already have one of their exteneded ones, with a 3" longer lever, for the followup rifle version with internal reservoir for retained air (ie PCP with onboard pump).... and I just got the tube and valve from Eric today.... Pretty funny, haven't even finished this one, and I already have plans for the next one....

    Bob
    WOW!!! that is a serious amount of air


    Maybe making a new head for the valve altogether and moving the check back slightly would allow for a bit more per stroke?

    I do the do same thing while making/drawing things up, get half way through something, and start thinking "Oh, I'll need that too" or "I should make three versions of this and see what difference they make"

    The on-board reservoir sounds pretty awesome as well, ill be watching it unfold closely
    "Just because you can, doesn't mean you should..."

  10. #10
    Moderator rsterne's Avatar
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    I'm making a whole new front for the Disco valve, which of course has no check.... I have to have an O-ring between the piston and the gauge port, and there is only 0.3" of room there.... However, that means the valve will be as long as the Disco valve and gauge mounting block combined.... and over twice the volume.... My goal is at least 5 cc.... A 13XX valve is 1.6 cc, and a 392 valve is about 4 cc....

    Bob
    Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
    Airsonal: Too many to count!

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