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Thread: QB78 Bulk Filling

  1. #1
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    Default QB78 Bulk Filling

    Guys

    Just bought the QB78D From Cor..Awaiting delivery. Anyone know if one can get the bulk fill adaptors locally. Would like to have it tuned, but for now I'm Ok with going Bulk Fill with under barrel paint ball cylinder. Any QB 78 owners on this forum?
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  2. #2
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    NickHok I know JTK did some tuning on them if I'm not mistaken.
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  3. #3
    REP: The Airgun Shop

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    Best option is to ask one of the engineering guru's here to make you a screw on valve that have a fitting for a paintball bottle or get a bulk fill adapter from Archer Airguns.
    Then you need a paintball bottle that is fitted with a hose and connector. You simply attach the hose to the bulk fill adapter and fill the rifle's air tube with CO2 (instead of those 2 CO2 canisters).
    When you are done, detach the hose, and off you go... you should get about 120 shots at 650 ft/s on a stock standard QB that is bulk filled.
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  4. #4
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    Heng Farmer!!! Ek sien nou eers jou QBs!!! Die Custom is 'n juweel!!! Hoe lyk die groupings met daai scope? het jy dit al oorweeg om bulk fill te gaan? Ek het iewers 'n adaptor gesien met 'n pressure gauge? 'n ou moet seker weet hoe vol om die paintball cans te maak...of kry 'n mens paintball cans met gauges??
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  5. #5
    Sharp Shooter

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    Hi NikHok

    Also a newbie with a qb78 from bulldog.co.za, no mods, just red dot scope and silencer.
    LOTS and lots of fun and very accurate out the box.
    Silencer make it viable to plink in backyard, also looks good. Sight is a nice to have but very nice to have . ;-)

    Would like a second in fact to try my hand at some of the tuning and bulk fills seen on internet searches. Charlie da tuna etc etc

    Let me know what bulk you go with and how it goes.
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  6. #6
    Sharp Shooter

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    Why dont you use air instead of Co2? You get less shots but very higher velocities. I think air might work out cheaper on the long run.....
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  7. #7
    REP: The Airgun Shop

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    Air works, but for safety stick to about 70-80 bar.
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  8. #8
    Sharp Shooter

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    No, I mean use 200 bar but with a different bottle. Dont use the Co2 bottle!!!!!

    You can expect velocities over 900 fps
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  9. #9
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    From what i've read the PCP converters out there also upgrade the internals to handle those kind of preasures. If you want to stay with the original inners you need to regulate the HPA tank to about 50-80 bar and use burst discs at both sides..just incase...Don't think it's worth it though unless there are tuners in SA that can upgrade the internals and fit a new tank for around 1,5K. Personally if I can bulk fill for much less than buying CO2 powerlets and maybe tune the gun to do around 750fps i can have myself a nice target rifle!!!
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  10. #10
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    I Found this very interesting article on the net for those who are interested. It seems even the built in cylinder can keep up!! Sorry IAN!!! Max pressure is around 300 bar. With safe operation around 150

    "Questions about PCP conversion of the QB78 have generally met with negative responses in UK forums. However the pressure cylinder of the QB78 is very similar to the cylinders on similar pump-up pneumatics from Crosman and others and it therefore seemed to me that the QB78 cylinder could safely be used as the basis for a similar relatively low pressure PCP to be charged from a hand pump. For those interested here are the results of my experiments.

    After stripping the gun and measuring the cylinder it was apparent that the total volume available would be quite Small - about 50cc including the volume of the valve chamber. The shot count between fills would therefore be low, but the trade off would be that less pumping would be needed between strings of shots.

    It was also clear that the metal of the cylinder was much thinner in the region of the threaded section at the fore end and that the original end plug made its seal in this region.

    I suspect that this may be the reason for any reported failures of the pressure cylinder when subjected to higher than CO2 pressures, but to be on the safe side I decided upon a hydraulic pressure test of the cylinder.

    A simple hydraulic pressure testing rig was formed by making a new front end plug to form a front seal at a point behind the threaded section of the cylinder and a travelling piston to fit the opposite end of the cylinder. The front end plug was fitted with a hydraulic pressure gauge and by filling the cylinder with water and forcing the travelling piston forwards using a two ton hydraulic jack with the parts located in a suitable cage I was able to apply pressures up to 400 BAR.

    From boiler technology the formula for the safe pressure limit of a seamless thin shell pressure cylinder is given by: p=t*2f/d
    Where p is the pressure in psi, d is the internal diameter of the tube in inches, t is the wall thickness of the tube in inches and f is the UTS of the tube material in lb/sq. in reduced by an appropriate safety factor.

    The QB78 cylinder has an internal diameter of 0.75 in, an external diameter of 0.865 in and appears to be made from bright drawn carbon steel. Assuming a UTS of 25tons/square inch which is between 20 tons for mild steel and 30 tons for low carbon steel this gives a pressure limit, ignoring the safety factor, of about 570BAR. Again from boiler technology it is accepted that the safety factor should be such that the cylinder does not expand by more than 0.1 percent of its diameter under the maximum working pressure.

    With this in mind I applied test pressures to the cylinder. It withstood an initial test pressure of400 BAR without damage. Then I applied pressures gradually increasing from zero, while carefully measuring the increase in diameter of the cylinder. At 300 BAR the increase was 0.00075 in, and so l determined this as the maximum limit.

    I then reassembled the gun as standard except that the new end plug was provided with a non return valve and a union for the attachment of a hand pump.

    Using an FX stirrup pump I Then tested the gun at various pressures to determine the power curve under pneumatic pressures

    Somewhat to my surprise l found that the power was quite consistent over a pressure range between 150 BAR and about 80 BAR. The following figures were obtained for a string of 22 shots, using Gamo TS18 18grain long range pellets straight from the tin.

    fps Ft/lb
    588.2 13.8
    584.8 13.7
    594.5 14.1
    601.7 14.5
    604.6 14.6
    606.8 14.7
    615.0 15.1
    606.8 14.7
    615.8 15.2
    615.8 15.2
    613.5 15.0
    612.0 15.0
    618.8 15.3
    606.8 14.7
    609.0 14.8
    606.8 14.7
    603.1 14.5
    606.0 14.7
    593.1 14.1
    594.5 14.1
    587.5 13.8
    575.4 13.2

    I am quite happy with this result for Spain, but if I were repeating this exercise to meet UK legal limits I would try to detune the gun by restricting the transfer port, reducing the hammer spring, or providing an internal valve opening restrictor similar to that of this BSA Ultra."
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  11. #11
    Sharp Shooter

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    Must say I find this all very confusing, R300 for bulk fill nipple from cor, than R 500 for slide quick disconnect from a paintball shop, than buy a cylynder dive/paitball , but than you have to get it filled, I hear you can modify a sodasteam bottle , now thats attractive as you get them at the garage shop 24hrs.

    Will take a long time at my backyard plink to break even, maybe after a tune it maybe a necessity. Or a prerequisite
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  12. #12
    Sharp Shooter

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    I think you are going to make an easy deployable plinker into something with it's guts dangling out. I had 2 QB79's so far. Apart from the CO2 canister they were the same rifles. One was tuned into a monster by JTK and the other STD. The tuned one guzzled CO2 which almost put it in the same shot count as a '78. That's why I kept the STD one to have loads of shots. They are loads of fun STD.

    I would say no to a tune up on these rifles. You can get a bearing/spring tipped screw that does wonders for the trigger. Costs R50. The rest imo is perfect for it's role. It's a plinker rifle imo which it does very well. Consider buying a different rifle if it's more power you need instead of tuning a '78/'79.
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  13. #13
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    Agree, i'm only doing a bulk fill on the deluxe, then i'll wait for a cheap STD to become available for tuning (just because one can)
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