QB79 Tuning

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DougP

Post subject: QB79 Tuning

Posted: Wed Dec 03, 2014 10:06 am

Joined: Thu Sep 11, 2014 10:59 am
Posts: 482
Location: West of Ottawa

Hi All,

My new chrony (let's not talk about what happened to my old one :oops:

) arrived yesterday and so my buddy and I spent some time measuring my QB79 (er, his - I've bequeathed it to him since he has a PAL until mine comes in - on it's way).
We were shooting Crosman hollowpoints which I think are 14.3g.
The 13CI tank started at 3100 PSI and ended after 100 shots at ~800. I just used the pressure gauge on the tank itself which I am sure is not very accurate but gives an idea of air consumption.
The pellet speed averaged around 845 FPS until shot 70 or so and then it started to drop. Still shooting above 600 at the 100th shot.
I don't have time to figure out how to put the two graphs together so I plotted them separately.
-Doug

Attachments:

QB79 Shot String.png [ 15.06 KiB | Viewed 1284 times ]

_________________
- Doug
.................
QB79 .177 (PCP) X 2

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rsterne

Post subject: Re: QB79 Tuning

Posted: Wed Dec 03, 2014 11:44 am

Joined: Sat Nov 03, 2007 4:19 pm
Posts: 9518
Location: Coalmont BC

I would assume from your graph the setpoint of your regulator is about 1500 psi, as that is the point where your velocity starts to drop.... Therefore, there is no point in shooting below that pressure.... Up to that point you have 70 shots averaging 845 fps (23 FPE) which is 1610 FPE total.... the pressure dropped 1600 psi (110 bar) which means you used 110 x 13 = 1435 CI total of air.... That is an efficiency of (1610/1435) = 1.12 FPE/CI, which is pretty good.... I wouldn't change a thing....

Bob

_________________
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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DougP

Post subject: Re: QB79 Tuning

Posted: Wed Dec 03, 2014 1:46 pm

Joined: Thu Sep 11, 2014 10:59 am
Posts: 482
Location: West of Ottawa

Thanks Bob.

I should have stated that this is the gun I bought off of Steve Barbas (Barbas929). He sold it to me with the mods done but the regulator set way down to non-PAL levels. I changed the washers to raise the pressure. I also replaced the bolt with a probed bolt I bought off of hacked2pieces. And I did a little bit more clean up of the valve.

Pretty pleased with the gun. Just put a Leapers UTG 3-9X50 scope on it. Looks very impressive now.
Still haven't shot it at a range or any distance longer than my shop allows. Waiting for my PAL to come in before I do that.

-Doug

_________________
- Doug
.................
QB79 .177 (PCP) X 2

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GarthThomas

Post subject: Re: QB79 Tuning

Posted: Wed Dec 03, 2014 2:08 pm

Joined: Sat Dec 17, 2011 10:04 pm
Posts: 616
Location: Goderich Ont.

Good idea

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When the chips are down, the buffalo is empty.

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barbas929

Post subject: Re: QB79 Tuning

Posted: Wed Dec 03, 2014 2:47 pm

Joined: Sat Oct 27, 2012 5:28 pm
Posts: 649
Location: st catharines ontario canada

I'm dying to see that thumbhole stock Doug...any pics of that beauty

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SlaviA 612/618/624/630/631
QB78D
79
Walther Falcon .25
Benji XL 1100

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DougP

Post subject: Re: QB79 Tuning

Posted: Wed Dec 03, 2014 2:47 pm

Joined: Thu Sep 11, 2014 10:59 am
Posts: 482
Location: West of Ottawa

uh, yes. Well, as I said, the gun is not officially mine at present. Now the question is - do I trust my buddy to give it back?

Hi Steve,
Here's a pic I had posted earlier with your scope on it...

Attachments:

rifle.jpg [ 55.68 KiB | Viewed 1229 times ]

_________________
- Doug
.................
QB79 .177 (PCP) X 2

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barbas929

Post subject: Re: QB79 Tuning

Posted: Wed Dec 03, 2014 4:17 pm

Joined: Sat Oct 27, 2012 5:28 pm
Posts: 649
Location: st catharines ontario canada

That is a real nice stock you made bud and it isn't exactly easy to do..well done

_________________
SlaviA 612/618/624/630/631
QB78D
79
Walther Falcon .25
Benji XL 1100

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Ace

Post subject: Re: QB79 Tuning

Posted: Wed Dec 03, 2014 4:38 pm

Joined: Mon Feb 11, 2013 12:46 am
Posts: 5706

Looks nice and its pretty efficient as well good job.

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"A candle loses nothing by lighting another candle"

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DougP

Post subject: Re: QB79 Tuning

Posted: Wed Dec 03, 2014 9:24 pm

Joined: Thu Sep 11, 2014 10:59 am
Posts: 482
Location: West of Ottawa

Thanks guys

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- Doug
.................
QB79 .177 (PCP) X 2

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