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Thread: My Version of the Millenium Pumper

  1. #1
    Moderator rsterne's Avatar
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    My Version of the Millenium Pumper

    A short while ago I built a .25 cal Carbine Pumper based on a shortened Disco Tube, the linkage from a Benji 392, and an MRod barrel.... While working on it, I started collecting ideas and parts for a rifle version using a full length Disco tube and a .25 cal choked Lothar Walther barrel.... Instead of having an auxilliary reservoir made from a 16 gr. CO2 bulb under the main tube, this gun would have an internal reservoir and a separate check valve.... After about a week in the shop, here are the main internal parts....



    The pump linkage is an extended Billet linkage from Mac1 Airguns.... It is stronger, and 3" longer than stock, although it maintains the same 7.6" stroke, giving a swept volume in the Disco tube of 54 cc.... I wanted to mount the pivot pin as far forward as possible, so instead of shortening the Disco tube I made a threaded end plug to help spread the end load of the pivot pin into the tube.... The smaller stub on the front will mount a barrel band.... The piston is the same as the one I made for the Carbine.... Immediately behind that is a check valve, sealed both sides with O-rings, mounted into two new holes in the Disco tube and secured with high tensile 8-32 low profile SHCSs.... There is a 2.5" long, full diameter, (18cc) air chamber between the check valve and the extended front end on the valve.... The valve extension is 3/8" ID for most of its length, providing additional volume, and enough wall thickness to mount the gauge and a male Foster fitting on the left side just behind the gauge location.... That will enable the gun to be filled from a tank or stirrup pump, both easier than the onboard pump, whose main purpose is for topping up in the field.... Also shown is an MRod trigger with Challenger trigger guard.... Everything will be mounted in a inletted Boyd's Blaster stock from Norm at Discos-R-Us in Nutmeg laminate....



    In the second photo are details of some of the parts.... The front plug was pretty tricky to machine.... I had to turn and thread it, mount it in the already slotted Disco tube, and then machine the slot and drill the pivot hole in the proper orientation.... It worked out beautifully, and the tube is full wall thickness at the pin location.... Below that is the check valve.... It is a simple aluminum housing, drilled through, and carrying a shortened check valve pin from a male Foster fitting, retained by a piano wire pin.... I tried one in my Carbine and it functioned perfectly, and the thin pin diameter left room for the screws on both sides.... Beside the check valve is the valve poppet and spring.... You can see how I have streamlined the head of the poppet, and narrowed the stem behind it.... The front of the valve spring has been expanded to 9/32" ID, to match the spring seat ID in the extended valve front end, for additional flow.... The brass part is a custom gauge mount I made from brass pipe fittings.... I used a 1/8" male to 3/8" female adapter and a 3/8" male to 1/8" female, then bored them out for additional volume, and threaded them together and sealed it with solder.... The Blaster stock is plenty deep enough for that assembly, and it added over 3 cc more volume to the valve.... The total volume is now 28.5 cc, slightly bigger than the Carbine was.... The Disco valve has been bored out inside to 0.62" ID, the throat drilled to 0.25", and the exhaust port milled out to 0.203" on a 20 degree angle.... It still needs a little TLC with a Dremel to round and smooth the inside corner.... The porting is 16% larger in area than what I used in the Carbine.... That combined with the longer barrel and slightly larger valve volume should gain a bit of velocity.... I'm hoping for about 10% higher FPE in this version at the same pressures.... With the additional leverage of the extended linkage, the effort should be the same at about 1800 psi as it was at 1500 in the Carbine.... so I have little doubt the peak power of this rifle will be higher....

    This project resulted from my joining the Green Forum because of interest in their "Millenium Pumper" project, the concept of which was to bring MSPs into the 21st Century.... There was no concensus of opinion over what it should be like, so I undertook this project as my own interpretation of what could be done easily, starting with mostly Crosman parts and adding a few custom bits into the mix.... There are lots of other interpretations of the idea possible.... this just represents mine....

    Bob
    Last edited by rsterne; Dec 01 2012 at 07:00 PM.
    Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
    Airsonal:
    .177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 22XX PCP 8-shot Carbine, 2260 PCP Rifle (50 FPE), Hayabusa PCP, .22 B-26, DAQ .308 Exile

  2. #2
    Administrator AirGunEric's Avatar
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    What? No consensus at the Green forum? There's a shocker!

    What does Mac1 charge for the longer linkage?

  3. #3
    Moderator rsterne's Avatar
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    He charges $60 plus shipping for the Billet lever in standard length and $5 extra for the 3" longer unit, IIRC.... It comes with the pins (piston pin is larger than stock) and a high strength steel link lever riveted in place.... You MUST use it with an adjustable piston (he makes those too, no idea how much, I made my own) as there is no spring to hold the linkage up and it must rock over center to lock in the up position....

    Bob
    Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
    Airsonal:
    .177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 22XX PCP 8-shot Carbine, 2260 PCP Rifle (50 FPE), Hayabusa PCP, .22 B-26, DAQ .308 Exile

  4. #4
    Senior Member SeanMP's Avatar
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    Very interesting Bob

    Any chance of a detail shot on that check valve? I like the idea of a self contained UBER MSP.

    I remember some SSP's having a funky vario cam system right at the hinge point so that the handle moved very little during the first 50% of the stroke. I'd like to find some drawings on that and maybe do some experimenting
    Sean

  5. #5
    Moderator rsterne's Avatar
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    The check valve is from a male Foster, sitting in a 0.161" hole and sealing against a 3/8" D milled pocket.... I drilled a small hole at an angle, inserted a bent piece of piano wire as a retainer (it's visible in the slot), and glued the other end into a pocket with JB Weld.... There are two 8-32 tapped holes in the sides 0.20" deep (ie not into the through hole) with milled flats for the heads of the screws.... The heads fit sungly in 0.270" holes in the tube.... There is a groove for a #113 O-ring in each end.... Easy-peasy....

    Bob
    Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
    Airsonal:
    .177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 22XX PCP 8-shot Carbine, 2260 PCP Rifle (50 FPE), Hayabusa PCP, .22 B-26, DAQ .308 Exile

  6. #6
    Moderator rsterne's Avatar
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    Well, it holds air!.... I got the main tube assembly done and pressured tested to 2000 psi.... I can actually still use the pump at that pressure, and it doesn't seem much harder to pump than the Carbine at 1500.... which means hard, but not impossible....



    I made and installed the hammer and the RVA, lengthened the rear of the bolt slot in the breech 0.10", faced 0.030" off the back of the valve and shortened the valve stem about 1/16" so that it is flush with the back of the valve when the valve spring goes coil bound.... Those modifications, along with the changes I made to the cocking slot in the tube and the bolt allow the maximum possible hammer travel, which works out to about 0.8".... No matter how the travel is adjusted, the cocking pin can't hit anything....

    There are basically two areas left to work on.... The Lothar Walther barrel has to be machined to fit into the breech, I have to make a chambering reamer and cut the chamber and a groove for the O-ring, make a .25 cal bolt, machine the transfer port and crown, and make a barrel band.... On the Boyd's Blaster stock, I have to cut a hole for the gauge and relieve a few spots for the MRod trigger.... and then the major job of converting the forestock into the pump handle.... The stock will then need final sanding an finishing.... I'm really looking forward to seeing how this new pumper will perform....

    Bob
    Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
    Airsonal:
    .177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 22XX PCP 8-shot Carbine, 2260 PCP Rifle (50 FPE), Hayabusa PCP, .22 B-26, DAQ .308 Exile

  7. #7
    Senior Member SeanMP's Avatar
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    Bob this project has my juices percolating

    What would your thoughts be on a 2 stage piston to keep the pumping forces reasonable and allow the pressure to be pushed even higher.
    I've was working on a bit of a sketch.
    2 stage pumper piston.jpg

    I just picked up a 30cal LW that would make a loverly MSP
    Sean

  8. #8
    Moderator rsterne's Avatar
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    Sean, I'm afraid I don't follow your sketch.... What is the large piston diameter and stroke, ie how much air can you move per stroke?.... I like the idea of a 2-stage pump but have never quite figured out an easy way to make one.... For anything bigger than .25 cal, the air usuage goes through the roof, so without one it would be a LOT of pumping.... If you move from 40 FPE to 80ish you need twice the air.... 120 FPE you are at three times.... assuming the same efficiency....

    Even with a .25 cal, I don't think I would consider a "pump and dump" knowing what I do now about how wasteful they are.... Once the pellet has moved more than half way down the barrel, all the air you use after that is basically thrown away.... These larger caliber MSPs end up being a PCP with an onboard pump for topping up in the field, IMO....

    Bob
    Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
    Airsonal:
    .177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 22XX PCP 8-shot Carbine, 2260 PCP Rifle (50 FPE), Hayabusa PCP, .22 B-26, DAQ .308 Exile

  9. #9
    Senior Member SeanMP's Avatar
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    My apologies Bob for offering up a half cooked egg.
    I have not set any stroke length or done the math to figure out what the minimum is. I was mucking about to see what the forces were at various pressures.
    Essentially the spring behind the large piston and the pressure relief are equal to the greatest force you would like to apply. Stroke length is whatever is necessary to achieve that pressure (say 1800psi) ideally just as the smaller piston enters it's bore.

    So at this point you have pumped the small bore to 1800psi. I have shown a one way check leading into the bottom of the small bore in case the small rod piston is in the bore before the large OD piston vents through the relief

    the smaller rod piston continues to compress the air into the reservoir check valve (not shown) and the only increase in force felt is the spring rate behind the large OD piston.

    I agree pump and dump would be an arm killer. I just didn't complete the sketch beyond the piston to show the check valve and reservoir
    Sean

  10. #10
    Moderator rsterne's Avatar
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    I completed the barrel work today.... I made a chambering reamer from O1 Drill Rod, hardened and tempered it, and then used it to cut the chamber to just past the transfer port location.... I then machined in the barrel port and a rebate in the end for the O-ring to seal the bolt.... It will be pinched between the barrel and the breech.... The barrel OD was reduced to 7/16" to fit the Crosman steel breech....



    The reamer has a 0.246" pilot that just rides on the lands in the LW barrel.... It has a 2* taper to create the leade, and then the chamber is 0.254".... The chamber is machined to just past the front of the transfer port, with the leade in front of that.... I also did a target crown on the muzzle....



    The barrel port is 0.188" wide by 0.219" long at the bore, tapering to a 0.204" circle where it mates to the transfer port, which will be made from a piece of 5/16" Teflon rod.... After finishing the machining, I used JB Bore Paste to lap the bore and the chamber, followed by a polish with their polishing compound.... The results are a mirror finish inside.... LW sure do make a beautiful barrel....

    Bob
    Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
    Airsonal:
    .177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 22XX PCP 8-shot Carbine, 2260 PCP Rifle (50 FPE), Hayabusa PCP, .22 B-26, DAQ .308 Exile

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