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 Post subject: Re: Meet QbBob QB78 FT
PostPosted: Fri Jan 18, 2013 9:00 pm 
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Joined: Wed Jan 05, 2011 12:35 pm
Posts: 5884
Location: P.G. B.C.
The chrony will record accurate velocities at whatever distance it will operate at, depending on the rifle or handgun used. If you get good readings right at the muzzle, great. If you have to move back a few feet, that's OK to, just realize you need a few fps velocoity buffer, just in case they measure your speed at the 'shoot' using one of the strap-on devices that measures at 1 1/2".

The actual velocity measured is the difference between the first screen and the second ie: the centre speed. Usually the greater the distance between the screens, the more accurate the measurement. My PACT timer has 2 screen space settings - 2' and 4'. Seems to me, the Oehler model 12 I had back in the 70's, was set up for 2 different screen spacings too, IIRC.

The reason 10' is suggested for most chronographs is that most work just fine at that range. This is to remove the muzzle blast shock waves from tripping the screens ahead of the bullet from a powder burning rifle.

Some rifles with really intense muzzle blast (large cased magnums shooting over 100gr. of powder like some WTBY's and Ultramags) give better readings even further out, like 20' to the first screen especially with the cheaper chronographes.

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 Post subject: Re: Meet QbBob QB78 FT
PostPosted: Fri Jan 18, 2013 9:01 pm 
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Joined: Wed Jan 05, 2011 12:35 pm
Posts: 5884
Location: P.G. B.C.
sholo wrote:
Jon wrote:
Lastly have you pressure tested that CO2 low pressure 1100psi max designed cylinder to 1 1/2 times intended operating pressure. You owe it to those around you.


No problem at all using a QB/AR tube @ 1500-1800 psi.

Todd


What about at 3,000psi, Todd?

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 Post subject: Re: Meet QbBob QB78 FT
PostPosted: Fri Jan 18, 2013 10:50 pm 
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Joined: Sat Nov 03, 2007 4:19 pm
Posts: 8936
Location: Coalmont BC
Anyone who designs a CO2 gun for only 1100 psi needs to give their head a shake.... CO2 tanks and cartridges are rated up to 120*F and the pressure at that temperature is 1900 psi.... The tanks are rated at 1800 psi MSWP, and fitted with a 3K burst disc.... The gun I made, which Frank bought, has a 1.8K burst disc fitted, which will fail at less pressure than what the gun could see on CO2 on a hot day or in the trunk of a car.... The math on the tube, assuming mild steel, has a safety margin of 3.9:1 at 1800 psi.... The regulator output is 1500 psi, well within what the gun could see on CO2....

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!
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 Post subject: Re: Meet QbBob QB78 FT
PostPosted: Sat Jan 19, 2013 7:56 am 
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Joined: Sat Apr 16, 2011 5:58 am
Posts: 495
Location: Eastern Ontario
Daryl wrote:
sholo wrote:
Jon wrote:
Lastly have you pressure tested that CO2 low pressure 1100psi max designed cylinder to 1 1/2 times intended operating pressure. You owe it to those around you.


No problem at all using a QB/AR tube @ 1500-1800 psi.

Todd


What about at 3,000psi, Todd?


Personally, I wouldn't - that's why I said "1500-1800 psi".

I'm no engineer - nor have I ever claimed to be - so if I'm wrong somebody PLEASE correct me as I don't want to post false information, but I'll take a stab at it and say that if the stock tube has a 3.9:1 safety margin @ 1800 psi (7020 psi), then theoretically (?) you should be able to use 3000 psi and still have a safety margin of 2.34:1 (tube only). Not sure if that is enough for me to feel comfortable with though, so as I said earlier: stay at 1500-1800 psi and you will have no safety issues...

Todd

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 Post subject: Re: Meet QbBob QB78 FT
PostPosted: Sat Jan 19, 2013 12:06 pm 
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Location: Coalmont BC
I would absolutely NOT use a stock QB tube at 3000 psi, not only is the tube wall thinner than that used on a Disco, but the screws that mount the valve and the backing block aren't up to the job.... When Frank is talking about using 3000 psi, he's talking about the pressure in the HPA tank, which is dropped down by the regulator to 1500.... Just in case the regulator fails, it is equipped with a 1.8K burst disc which will blow and prevent the gun from ever seeing more than 1800 psi, even with a regulator failure....

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: Meet QbBob QB78 FT
PostPosted: Sat Jan 19, 2013 12:15 pm 
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Thanks for the explanation, Bob - this stuff is all a learning experience for me.

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 Post subject: Re: Meet QbBob QB78 FT
PostPosted: Sat Jan 19, 2013 1:43 pm 
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Joined: Sun Nov 06, 2011 2:16 pm
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Location: 1/2 Way From Ottawa and Montreal,
wow I get to my PC and I got a ton of questions thanks for helping me guys.


I will re-chrony QbBob to 6" from Barrel to 775fps with JSB's 8.44g


Now for the big news.

CAPS ON

I GOT IN MY LOCAL GUN CLUB TAKING THE COURSE NEXT SATURDAY!
I'm so happy this is a 50 yards in doors heated club yes heated.
I will practice so much I will be even better I will take my Disco and QbBob and test witch is best.

and this club is 2 streets from me take me like 10mins to get there. I can practice 6 days a week no Sundays.

and I can bring a +1 so cool.

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 Post subject: Re: Meet QbBob QB78 FT
PostPosted: Sat Jan 19, 2013 8:36 pm 
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Location: P.G. B.C.
Have fun - I know I would. Unfortunately, we can only get 25 meters indoors max.

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 Post subject: Re: Meet QbBob QB78 FT
PostPosted: Sun Jan 20, 2013 8:54 pm 
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Joined: Fri Sep 09, 2005 11:55 am
Posts: 231
Location: England.
I wouldnt be surprised at that figure Todd but 3000psi is an entirely different matter.
These tubes were designed to operate at no more than 90bar (1300 psi) or the CO2 would freeze, then of course the safety factor hopefully added on.
Just so anyone is aware more than anything, the dangers of high pressure air cannot be seen and always ignored. Its on par with a oxy acetylene bottles at 232bar plus safety factor built in (4500 psi+) is what i am on about here put in to untested tubes to operate up to 90bar (1300 psi.)

Not alone there are far worse from asia even thinner wall thickness and minimal threads holding end plugs in.


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 Post subject: Re: Meet QbBob QB78 FT
PostPosted: Sun Jan 20, 2013 9:02 pm 
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Joined: Fri Sep 09, 2005 11:55 am
Posts: 231
Location: England.
At least some efforts been made Bob by using a bust disc. Must say even some very well known manufacturers have over looked this and literally put one full thread holding reg on to knock open valve - but what if reg pressure increased!
Not the cure two wrongs dont make a right.


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 Post subject: Re: Meet QbBob QB78 FT
PostPosted: Sun Jan 20, 2013 9:24 pm 
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Location: Coalmont BC
Quote:
no more than 90bar (1300 psi) or the CO2 would freeze

I have NO idea where you got that from, but it's completely false....

Image

In our airguns, below 31*C, CO2 exists as a liquid and a gas in equilibrium.... Above that, it exists as a supercritical fluid, which in turn acts like a gas for the most part.... For CO2 to "freeze" even at -20*C would require 1000 bar.... at 100 bar, it would have to be below -40*C....

If you have specific data on the QB tube that states it was designed for a MSWP of 1300 psi, please present it....

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: Meet QbBob QB78 FT
PostPosted: Mon Jan 21, 2013 6:30 am 
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Joined: Sat Apr 16, 2011 5:58 am
Posts: 495
Location: Eastern Ontario
Jon wrote:
These tubes were designed to operate at no more than 90bar (1300 psi) or the CO2 would freeze


OK, I realize that I may not be the sharpest knife in the drawer when it comes to figuring out on my own the MSWP of a tube/valve setup, but that doesn't sound right, even to me! Everything I've ever read/researched on the subject (by people a hell of a lot smarter than me) has indicated that the steel tubes can safely handle 1800 psi, as it has been well documented that Co2 can easily reach this pressure on a warm day, so why design a tube that falls 500 psi short of that mark?

My AR2078 has a 13 ci bottle attached (with a 1.8k burst disc) regulated at 1500 psi, and the gun has been charged at this pressure constantly for a little over 9 months straight now with absolutely no problems whatsoever. Tube hasn't "swollen", valve hasn't moved, nothing. It is still as it was the day I bought it...

rsterne wrote:
If you have specific data on the QB tube that states it was designed for a MSWP of 1300 psi, please present it....


I would be interested to see that as well...

Todd

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PostPosted: Sun Feb 17, 2013 1:58 pm 
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Joined: Sun Nov 06, 2011 2:16 pm
Posts: 1631
Location: 1/2 Way From Ottawa and Montreal,
so I ajusted QbBob at about 20fpe at Muzzle 1008fps

filled the tank up to 3000psi I'm regulated at 1500psi [ on back up tank, QbBob's tank is Regulated at 1600psi ]
instal my back up scope on it Bushnell 4-12 x 40 AO just to do some test, My usual Scope is a Zos 10-40X60.
got a new tin of JSB's Exact Diabolo 8.44g
took it to my local gun club with interior range of 50 meters.
set up and ajusted the scope at 10 meters 25meters was all 1 hole in one's I was super happy.
so I set up a taget at 55yards about 50 meters, and started ajusting my scope at 55 yards my scope was at the max
and I could not see my target clearly but I ajusted it the best I could and I was able to group dime size made me very happy.
so after ajusting the scope I was shoting the lines on the paper targets was so good I told the guys hey look I will cut the string holding my target,
so I took one shot and cut the string, I was estatic really happy of my setup. but it took 3 shots to cut 2nd string it was bigger and stronger I was hitting it.
so one of my friend is the with a over 3000$ .308 and he tell me he can group better then me at 50 yards so we made a chalenge and took 5 shots and I had the best tightes
groups for my 5 shots and better then 1/2 of his woot made me happy.

so now for FT it's all up to me I know my airgun can do there part now I must do mine.
I would really like to hace my Zos 10-40X60 scope setup and work perfect on QbBob but it seems like I just can't dail it in proprely
maybe it's me or scope is defective. but the Bushnell 4-12 x 40 AO is doing a good job for now.

Anyone up for a little competion LOL

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Custom Design by ME PCP/HPA Air Carbine 10-50X60 Scope My 2018 FT Open


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