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 Post subject: HPA QB78
PostPosted: Sun Aug 18, 2013 1:03 pm 
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Joined: Thu Aug 02, 2007 7:54 pm
Posts: 356
Location: Quebec, Canada
I was looking at this adapter and was wondering if it fits directly on without any mods? http://scopesandammo.com/storefront/pro ... -cap-p-832 i was thinking of using a T fitting and mounting an air pressure gauge on one side and a quick connect on the other, and how many psi max should i fill it to?

Thanks


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 Post subject: Re: HPA QB78
PostPosted: Sun Aug 18, 2013 1:48 pm 
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Joined: Sat Nov 03, 2007 4:19 pm
Posts: 8973
Location: Coalmont BC
That adapter is designed for CO2 but will work with HPA providing you don't use too high a pressure.... On a QB78 I wouldn't use more than about 1200 psi without taking the gun apart and making sure the valve is sitting up tight against the steel backing block and shimming it if necessary.... Once you know that all three screws are sharing the load properly, you can use about 1600 psi safely.... However, going past 1200 may require you to shim the hammer spring preload or the velocity will decrease above 1200 psi....

If you use a "T" fitting, make sure you get one intended for hydraulics, don't use one made for gas lines or plumbing, they are not intended for the pressures involved in HPA.... You don't strictly need a gauge on the gun, provided you have one on your pump or tank you are filling from, you can use that to fill your gun to your working pressure.... Eric can supply you with the proper male QD fitting to connect to your pump or tank.... and also the fill station to work with a SCUBA tank is that is what you decide to use.... You will have to be careful not to overfill from a SCUBA tank as they run at 3000 psi, and you DON'T want that much pressure in your gun....

I don't know what you are expecting for shot count from a QB78 running on HPA, or for velocity, but right off the bat, it will be PAL rated unless you detune it.... I got the following combinations of velocity and shot count, using 14.3 gr. pellets, filling to about 1300-1500 psi, depending on the modifications I made (stock hammer spring preload)....

23 shots at 590 fps.... 13 shots at 690 fps.... 5 shots at 820 fps.... shots within 4% ES (velocity range)....
34 shots at 580 fps.... 18 shots at 680 fps.... 9 shots at 810 fps.... counting all shots with 10% ES (1400-1600 psi fill)....

As you can see, the shot count drops drastically as soon as you modify the gun for more power.... Using a 10% ES is only good for shooting at less than 25 yards, a 4% ES is good to about 50 yards before the POI changes too much....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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 Post subject: Re: HPA QB78
PostPosted: Sun Aug 18, 2013 1:57 pm 
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Joined: Thu Aug 02, 2007 7:54 pm
Posts: 356
Location: Quebec, Canada
alright then ill drop the idea from my head :P seem a bit to much of work for not much


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 Post subject: Re: HPA QB78
PostPosted: Sun Aug 18, 2013 9:57 pm 
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Joined: Thu Feb 02, 2006 11:35 pm
Posts: 3099
Location: Alberta Canada
patfraser3 wrote:
alright then ill drop the idea from my head :P seem a bit to much of work for not much


Yes you should for on the DARKSIDE we have cookies...he he he... Sorry couldn't resist...

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May the cry of the pack be with you upon your hunt

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 Post subject: Re: HPA QB78
PostPosted: Tue Aug 20, 2013 6:45 pm 
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Joined: Mon Mar 09, 2009 6:46 pm
Posts: 1395
Location: r Alberta
He White Wolf all I got was coffee. You must have eaten the cookies.


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 Post subject: Re: HPA QB78
PostPosted: Tue Aug 20, 2013 6:57 pm 
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Joined: Thu Aug 02, 2007 7:54 pm
Posts: 356
Location: Quebec, Canada
Plasticman wrote:
He White Wolf all I got was coffee. You must have eaten the cookies.


everything is gone i dont drink coffee so i gave it to you, but he robbed my cookies so i couldnt give them out...


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