More 1250 PSI HPA thoughts (another long one)

[ribbonstone]

Would be a WHOLE lot better to get a new air tube, made for high pressures. It's not that MOST QB tubes won't handle 1250PSI, but that SOME won't...and you really can't tell which ones will have a problem by looking at them. Even if the odds are with you, it is still a gamble...so no *_*_*_*_*_*ing about losing an eye or ruining a good gun if your guessed wrong.

IF you do decide to try over 850PSI and want to use the stock QB tube, would do three things:
(1) Add two more set screws to the valve...if something is going to come lose and let high pressure gas jet out, would be better if it was at the muzzle end.


Retaining screws though QB gas tube and into the valve head, one per side. Keep them to the REAR of the o-ring that seals the valve to the gas tube, about even with the existing retaining screw (on the bottom). Thread size not real important, but 8-32 or 6-32 cap screws are easier to find than other threads. It's not that they'll back out, a touch of lock-tite will take care of that, are there to keep the valve from being forced backawards by high pressure.

(2) Change to a Delrin valve seal (believe Mounatin Air sells them if you can't make one). The issue valve seals are a little soft for constant use at this pressure.

(3) Add a RAP 4 gauged on/off between the HPA tank and the rifle.
RAP 4 on/off.


Can read the HPA tank's gauge as 2,500PSI, the gun pressure as 1250PSI (actually, it looks more like 1200PSI), and see the large brass 1.8K burst disk

The gauged on/off does several things.
1)The gauge on the on/off reads the GUN side pressure, so you'll know what the output pressure of the regulator really is. Bad news is that one HPA tank sold (not from a sponsor here) as a 1100 output blew the RAP4 gauge...that gauges goes to 1500PSI, so what the real output was is anybody's guess. That regualtor is beat to snot and in the junk box.
(2)Can store the rifle with it on "off", which makes finding leaks a bit easier...if the gun side pressure drops over night, the problem is with the gun...if the tank pressure drops over night, problem is with the HPA tank. One of the reasons HPA generates more vel. at the same pressure as co2 is becasue air is "thinner" and flows more easily....those same features usually mean it finds leaks sooner as well, so expect to hunt down a few slow leaks when you first convert to HPA.
(3) Can turn the gun to off, shoot it once, and store the rifle with 200-500PSI pressure in the rifle to seal the valves but not have to store it at full HPA pressure.
(4) The ON/OFF has 1.8K burst disk. The HPA tank regulator should have two burst disk, one on it's high pressure side (usually a 4.5K disk) and one on it's low pressure side (usually a 1.8K disk). With the on/off, have TWO 1.8K disks on the low pressure side....which might vent enough air if the HPA tank screws up and dumps all 3K at once.

The one QB running on 1250PSI is a custom .25cal (with the three mods mentioned above). On co2, it will earn 23 foot pounds. On 850HPA will earn 25.5 foot pounds. On 1250HPA, will earn 32.5 foot pounds (this would be 30.7gr. Kodiaks at 588fps / 612fps/ and 690fps).

Truth be told, nothing I've shot with the .25 could tell the difference between 25.5 foot pounds and 32.5 foot pounds and it's going to be converted back to 850PSI after a few more experiments.

The two other HPA QB's are running 850PSI, one still running fine on a stock valve stem...neither of those two have had the extra retaining screws added. No problems with them at 850PSI pressure so far.

BUT by goofing around with HPA and stock QB tubes, if I have to relearn to shoot left eye dominate becasue I blew my right eye to jello-goo, I've no one to blame but myself.

Left to right:
Standard QB78-22 with little done to it. Runs on 12gr. or bulk co2. As issued, getting 10.9 foot pounds.
Max effort QB78-25. Running on 1250PSI HPA for 32.5 foot pounds (but abpout to go back to 850PSI).
Carbine QB79 - 22. Running on 850PSI HPA without any troubles. Set for 12 foot pounds, about like a stock Benjamin with 7 or 8 pumps.
AR 2078 - /177. Set up to be slow and quiet. Running on 12gr. or bulk fill co2. gettin aboput 8.5 foot pounds.
QB78 - .20. Running on 850PSI HPA with out any trouble. Set a bit hotter than a Sherican would be, geting 15.7 foot pounds.

[tonaka]

Thank you for the nice report Robert!
It is in my plans to eventually convert my QB79 to HPA but if I do that I would naturally like it to shoot faster. I just like power. I think I will try 1250PSI output anyway. Pretty scary though if tube blows. How many shots did you get with this pressure output? And where do you buy RAP4 gauge?

[ribbonstone]

From RAP 4 (Real Action Paintball):
http://www.rap4.com/paintball/os/onoff-adapter-with-gauge-p-1531.html

IF I were to do this again, would probably go with a 1000PSI output (believe  jbsairman.com could make a 1000PSI output) and live with a little less velocity.  Was serious about the comment, really doubt that game would know the differnce between that .25 pellet at 612fps (with conservative 850PSI out put) or at 690fps (with 1250PSi out put)...either way, get a puckered entrance and a star pattern exit.

As a good hunting buddy said, "Making the pellet exit the far side of a critter going faster doesn't seem to do jack."

One of the things about higher output is that you generally stop shooting  before you reach the output pressure.  So with a 1250PSI output tank, will stop shooting at something near 1400-1500PSI...which gives you about 1500PSI for shooting.  With 850 out put, will stop to refill at something near 900-1000PSI (which gives me 2000PSI for shooting).

Like anything else, it takes gas to go fast.  That .25 eats up a lot of air per shot at the over 30 foot pound level; a 13CI tank will give about 37 good consistent shots.  The midly tuned 850PSi QB79 running on 850PSI will get a bit more than double that.

[Jaymo]

Where can I buy an HPA tube for a QB78?  I have one of the TF78T(QB79?) variants. I have thought about converting it to HPA for wintertime. I've pumped my QB78 Deluxe .177 to 1100 psi with my Axsor pump. Get about 6 really good shots before velocity drops. At around 10 shots, they fail to make it to the target. It only takes 20-21 strokes of the pump to achieve this pressure. That's the highest I'll go with a stock tube, since CO2 only gets up to about 1,150-1,200psi in the heat of summer in GA. I've pumped it to 900-1,000 psi more often than I have to 1,100. Haven't shot it much that way, since I haven't installed the extra valve retaining screws, yet. I had thought about drilling a hole through the tube/valve close to the bottom of the tube, for a roll pin, instead of screws. That way, I have more support/restraint for the valve via more surface area contact between the pin and the valve. Makes it a little more of a hemorrhoid to remove the valve, unless you have roll pin punches(I do). Then again, once it's tuned to my liking, I won't be pulling the valve unless necessary. And I plan on tuning it before drilling/pinning it.

[Jaymo]

Nothing against your method, of course. It's a good, proven method. Mine is another proven method. Not better, not worse. Just different. I hate tapping #6 and #8 screw holes. Very easy to mess up.

[ribbonstone]

Don't see why the pin wouldn't work...believe it wouldn't be easier, but at least you won't have to tap and drilling like this is best done on a drill press.

Don't know how others do it, but I'll strip the gun completely.  Mount the valve (using the one factory screw) and then drill/tap through both the tube and the brass valve head at the same time (want the least 'slack" possible). Brass really wants to grab the tap, so use coat it in bee's wax (and don't forget to de-grease after tapping).  Usually wrap the tube with masking tape, which lest me measrue and fiddle getting the screws marked for the right place.

Couldn't find anything but my starter tap.  So taped the holes with it (only getting one thread becasue of the taper) then cut/ground the tap to a "plug" and tapped to the bottom.  Also couldn't find short 8-32 cap screws, so had to cut the long ones down to size.