2078 on HPA

I successfully pumped my AR2078 with the Benji pump and did some tests in my garage 10 yd range, it's cold and rainy here today. I emptied the CO2 from the AR2078, and pumped it up to 1000psi. It takes 22 strokes to fill it from empty to 1000 psi (recommended safe limit), then I got 5 shots in the same hole at 10 yards (power is initially high and then falls about 25fps/shot), 5 more shots within 1/4" drop giving a 10 shot group in a 1/2" square. Then the next 2 shots are noticeably low by 1/4" each and it dies after that. There were only 16 pump strokes to fill it to 1000 psi after 12 shots taken. And the effort is about the same as a bicycle pump, so you can say 3 pumps = 2 shots, nearly the same as a SSP rifle like the Daisy 853. http://www.airgunforum.ca/forums/ima...on_biggrin.gif

Next step is to run it off a tethered regulated HPA paintball tank. How should I detune this to make sure it runs at non-PAL speeds? I have a icemaker TP seal in it and it runs hot. I experimented with different TP seals and I can get it down to 380 fps on CO2 ... but is it way inefficient to slow it down with restricting the TP? Is adjusting the hammer spring the way to go instead? Advice appreciated.

This is so much fun... I forgot for a while I still have to do work and taxes....Doh.

Restricting the TP is a good way to go to control the velocity as it produces a flatter shot string than using the hammer spring.... However, if the hammer spring it WAY too strong, it will waste air, so you have to get that in the ballpark first for maximum shot count.... Here are my results for HPA on a QB78....

http://i378.photobucket.com/albums/o...B78Initial.jpg

IMO you don't need to hold yourself to 1000 psi, as CO2 can easily go to much higher pressures in high temperatures.... At 120*F, it reaches about 1900 psi.... That will produce very low velocities in a QB.... you will note that the stock hammer spring peaks at about 1100-1200 psi on HPA and then the velocity starts to drop.... I'm not saying to pump to 1900, but 1400 psi shouldn't be an issue, and if you take the gun apart and make sure the valve is tight up against the steel block that mounts the breech and the stock bolt you will be OK up to about 1800 psi or so, providing you don't pressurize the gun without all three screws in place....

Bob

If you're using a regulated, tethered paintball setup on HPA- adjust the regulator. As a result of it being regulated, you could put the pressure down as low as 450psi or as high as 2200psi- this way you can control the gun's output power based on the input pressure. If you end up below 850psi on the regulator, it means someone could fill it with Co2 and it is a "firearm" - so the idea would be how to put 1000psi into it and still keep it below 500fps- i.e. your previous idea and Bob's input.

FYI, 850 psi on CO2 is usually slower than the same pressure on HPA.... I find about 700 psi on HPA is equivalent performance to CO2 at 70*F....

Bob

I'm in agreement with Bob. First decide what is comfortable and convenient for you to fill too. 1500-1600 psi is what I run but follow Bob's advice and make sure the block is snug to the valve and that all the bits are free of combustible oils. Silicone grease is the way to go when playing with HPA.

Then get in the ballpark with hammer strike

Then use restriction to set your velocity. If your already using poly tubing then switching to 1/4" teflon rod with a hole drilled in it isn't much of a leap.

The nice thing is once you get it this dialed in your velocity will be very solid at a broad range of fill pressures.

As a rough starting point I am set at the following right now for a .22 barrel

1600psi fill
Hammer strike 0.065 less than stock
0.057" Transfer port

velocity is 498fps avg from 1600 to 600 psi

I broke down and bought a 48 ci reg'd HPA tank. It is Guerrilla brand, paintball shop owner couldn't tell me what the reg was set to, it has a 1,8k low pressure burst disk.. so I believe it will be 800 or 850 psi. I'll post pics and results soon. Very busy with work work so I only get moments these days to play.

This tank:
http://www.paintball-discounters.com...i-hpa-tank.htm

A "non-specified" output pressure is always 850psi- you only get large variations from this when the bottles were specifically done otherwise- as they are intended for paintball Co2 use- 850psi is the thing.

Thanks Eric, I did find it on the googlenet... 850psi it is.
It shooting hot of course, but consistent with an ES of 6 fps over 10 shots. Also, it is running about 50 fps higher than when I last chronied it on CO2 (65 F or so). It seems to be louder than on CO2.
I had time for about 50 pellets, tried a few, and the usual suspects are grouping well at 10m even CPHP that didn't do so well on CO2. The tank dropped from 3000 psi to about 2500 psi over the 50 shots though... I'm surprised. Anyhow Benji hand pump - 60 strokes had it back up to 3000 psi.