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Thread: HPA converted SMK QB78

  1. #1
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    HPA converted SMK QB78

    I have been given a QB78 that has been converted to air , the shop took it in and have found it was leaking .I have now fitted a set of seal but im not sure what is the safe filling pressure.
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  2. #2
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    Bottle is usually a 200bar bottle fitted with a regulator set at 1000psi.
    Two burst discs will confirm its a regulated bottle.
    Bottle neck should state working pressure.

    No burst discs may indicate a co2 bulk fill bottle.
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  3. #3
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    Quote Originally Posted by venoman View Post
    I have been given a QB78 that has been converted to air , the shop took it in and have found it was leaking .I have now fitted a set of seal but im not sure what is the safe filling pressure.
    Details on the conversion would make it easier to give an exact answer.
    Too many airguns!

  4. #4
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    As has already been stated, we need to know more. If it has still got the original gas chamber then it is only safe to about 1000psi.

  5. #5
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    At 26 C the CO2 is already at 860 p.s.i. and at 30 C at over 1000 p.s.i. So the QB78 would have a safety factor allowed when used in hot countries. Using HPA at low pressure is not very efficient as the pressure drops very quickly on each shot, and velocity drops. The best way now that it has a bulk filling connection is to use bulk fill CO2 from a fire extinguisher as you are filling with liquid CO2 which will last for many shots. Tried it with my 111, very few shots compared with CO2.

    Baz

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    Last edited by Benelli B76; 19-03-2023 at 08:13 AM.
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  6. #6
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    found that interesting

  7. #7
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    Quote Originally Posted by On-the-target View Post
    As has already been stated, we need to know more. If it has still got the original gas chamber then it is only safe to about 1000psi.
    Its all standard apart from a conversion on the front cylinder cap . its very awkward filling it with fingers in both ears.
    Last edited by venoman; 19-03-2023 at 10:12 AM.
    .22 Venom Mach 1 (FAC) 6-25x56 Millett.
    .22 Venom Mach 2 Thumbhole 6.5-20x40 Leupold EFR.
    .22 Venom Mach 2 Sporter 4-12x40 Leupold.
    .177 Venom Vantage 4-16x50.
    .177 Venom Daystate 8-32x56 AGS.
    .22 Venom Datstate 4-16x56 AGS.
    .22 Webley Venom FX2000 6-18x40 Busnel Legend.
    .177 Titan MPT by Steve Pope 6-24x40 Tasco.
    .177 Pro-Sport 4-16x50.
    .22 Webley FX2000 3-9x33 Leupold EFR.
    .177 Logan Solo 4-16x50.
    .22 HW90 (spring powered) 4-16x50
    .22 Gamo Stutzen.
    .177 Walther lever action.

  8. #8
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    Quote Originally Posted by Neil54 View Post
    Bottle is usually a 200bar bottle fitted with a regulator set at 1000psi.
    Two burst discs will confirm its a regulated bottle.
    Bottle neck should state working pressure.

    No burst discs may indicate a co2 bulk fill bottle.
    Your thinking of the QB79 with the 88 grm screw on cylinder, this is the QB78 that you put two 12grm C/O2 bottles in.
    .22 Venom Mach 1 (FAC) 6-25x56 Millett.
    .22 Venom Mach 2 Thumbhole 6.5-20x40 Leupold EFR.
    .22 Venom Mach 2 Sporter 4-12x40 Leupold.
    .177 Venom Vantage 4-16x50.
    .177 Venom Daystate 8-32x56 AGS.
    .22 Venom Datstate 4-16x56 AGS.
    .22 Webley Venom FX2000 6-18x40 Busnel Legend.
    .177 Titan MPT by Steve Pope 6-24x40 Tasco.
    .177 Pro-Sport 4-16x50.
    .22 Webley FX2000 3-9x33 Leupold EFR.
    .177 Logan Solo 4-16x50.
    .22 HW90 (spring powered) 4-16x50
    .22 Gamo Stutzen.
    .177 Walther lever action.

  9. #9
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    it's bulkfill co2 not air i'd say and SHOULD NOT BE FILLED WITH UNREGULATED AIR ABOVE 1100PSI-they start to get valve lock around 1250psi anyway
    you can get pcp tubes but without much alteration the 78 isn't suitable for air unless it is regulated fed by a paintball bottle or similar
    if it's a std length cylinder it will just have the cap which could be a converted original a Gmac one a Porky Yorkie or one of mine
    if it is a long tube one then porky yorkie came up with them to be either bulkfill or 4 caplet(the robber copied his idea when he was a member of UKCAF and why he isn't well regarded by most on there)
    if the cap looks to be an original steel one with just the foster fitting added them it will likely be a dual bulk or capsule one
    if it has a brass inner with a std steel retainer it's probably a gmac half conversion
    if it has a brass retainer and inner a full gmac one
    if it has a brass retainer with aluminium inner(some i anodisedblack) and two orings it could be one i made

  10. #10
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    I agree it sounds like a bulk fill end cap.
    You can fill it compressed air to 1000psi. You will only get 5 shots.
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  11. #11
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    Could someone please explain the benefits of conversion from Co2 to air?

    Cheers, Lawrie
    Last edited by Lawrie Amatruda; 20-03-2023 at 07:22 PM.

  12. #12
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    Quote Originally Posted by Lawrie Amatruda View Post
    Could someone please explain the benefits of conversion of Co2 to air?

    Cheers, Lawrie
    There's nothing wrong with CO2 for even the above the average shooter!
    Walther CP-2 Match, FAS 604 & Tau 7 target pistols, Smith & Wesson 6" & 4" co2 pistol, Crosman 1377,
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  13. #13
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    Quote Originally Posted by Lawrie Amatruda View Post
    Could someone please explain the benefits of conversion of Co2 to air?

    Cheers, Lawrie
    i don't think there is on a 78 unless you're using a remote tether from a large regulated cylinder from a static position
    the 78 imo is better on co2 ,bulkfilling only brings the cost down
    the 79 now is better with a 13ci paitball tank fitted -very large shot count and fps spread is very low,nothing really req to alter on a std gun(i personlly swap the gas block bolts to UK sourced ones

  14. #14
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    Quote Originally Posted by Lawrie Amatruda View Post
    Could someone please explain the benefits of conversion of Co2 to air?

    Cheers, Lawrie
    Cheaper to fill.
    Not prone to power fluctuations with temperature.

    I like mine on CO2 12g capsules.
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  15. #15
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    Oh yes, more shots per fill.
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