4500PSI, REGULATED, AIRGUN PROJECT
PLAYING AROUND WITH HIGH PRESSURE AIR AGAIN.
BUILT A 3 CUBIC INCH AIR CHAMBER THAT HAS A VALVE IN IT.
IT SCREWS INTO THE REAR OF THE GUN, JUST LIKE A TANK.
PIPED AIR TO THE REAR OF THIS CHAMBER USING 1/8 INCH, STAINLESS STEEL TUBING.
CONNECTED THE OTHER END OF THE TUBE TO MY COMPRESSOR AND CRANKED IN 2000 PSI.
SHOT A FEW .25 CAL, KODIAK PELLETS INTO A 2 BY 4, THEY WENT OVER 3/4 OF THE WAY THROUGH — STILL GOOD POWER WITH ONLY 2000 PSI.
SEE THE PICTURE OF THE ADJUSTABLE REGULATOR.
IT WILL SCREW INTO MY 68 CUBIC INCH, 4500PSI TANK. THEN I WILL MOUNT THE TANK UNDER THE SHROUD, AHEAD OF THE TRIGGER, AND PIPE THE REGULATED AIR INTO THE 3 CUBIC INCH CHAMBER.
COMPLETED THE 2000 PSI TEST THIS MORNING USING THE COMPRESSOR.
IT WAS SUCESSFUL, SO I ORDERED THE REGULATOR OFF EBAY FOR $22 DELIVERED.
NEXT I GOTTA SEE IF I CAN CRANK THE REGULATOR UP TO 2000 PSI.
WHEN I SHOT THE 2 BY 4, THE GUN SEEMED MUCH QUIETER.
MAYBE IT INDICATES BETTER AIR EFFICENCY – LESS EXCESS AIR BLASTED OUT THE MUZZEL. THE TUBING HAS A VERY SMALL I.D., SO THE 3 CUBIC INCH CHAMBER DOES NOT REFILL INSTANTLY, LIMITING EXCESS AIR BLASTING OUT THE BARREL??
SHOT OVER CRONY WITH VARIOUS PRESSURES. 24 INCH BARREL,31 GRAIN KODIAKS
1000PSI — 570 FPS
1500PSI — 700 FPS
2000PSI — 900 FPS
2300PSI — 940 FPS
THE VALVE / GUN COMBO NORMALY IS TUNED DOWN TO 950 FPS AT 3000 PSI (FOR ACCURACY). THIS VALVE IS SETUP FOR 3000 PSI. I AM SURE I CAN BUILD A VALVE FOR 2000 PSI THAT WILL GIVE FULL POWER, AND THEN SOME.
I BELIEVE THE 3 CUBIC INCH CHAMBER IS TOO BIG AND CAN BE CUT DOWN IN SIZE.
THE 3 CUBIC INCH CHAMBER IS BUILT FROM 1.5 INCH DIAMETER, 2024 AIRCRAFT ALUMINUM. IT HAS A .3 INCH THICK WALL, SO THERE IS PLENTY OF STRENGTH FOR 4500 PSI. USING BARLOWS FORMULA- IT SHOULD BE GOOD FOR 24000 PSI BURST PRESSURE.
THE BRASS PLUG IN THE END OF THE CHAMBER IS THREADED 3/4 INCH – 10 THREADS PER INCH AND “O” RING SEALED.
All Replies
Lama:
That tank mount is built for a 68 cubic inch 4500 psi tank. Ill bet you could shoot all day on that. I was using the small tank for testing only. Havent done any shot count runs yet, but its gotta be good on air.
Mark
Shadoh:
I built the first 3 cubic inch chamber out of 7075 aluminum.
I think the round stock I am using now is 1.5 inch round 2024 aluminum.
Actualy I made 3 different chambers. Started with 3 cubic inch, and it was too big. The chamber I am using now is about 1.5 cubic inch. The pressure drops 300 or 400 psi after each shot. I think that is about right.
The smaller chamber size allows a much thicker wall, so I know I am way safe.
The high pressure tube I use has a very small i.d. , so the chamber refills slowly – enough time to read the pressure gauge.
1.5 cubic inch chamber, with a .25 cal barrel seems about right. You could go a little smaller with a .22 cal barrel.
Machining a deep chamber is kinda hard. There is a valve end hole and a “back end” hole, both are smaller than the inside of the chamber. You gotta have just the right shape boring bar. I am using a valve built for a paintball tank. It is threaded 5/8″-18, I think.
I dont take deep enough cuts to heat up the aluminum, but heat WILL change the temper and mess up the tinsile strength. You gotta be carefull to leave a smooth, large radius on the inside of the chamber. Sharp corrners cause “stress risers” effectivly lowering the tinsile striength of the material by a factor of 2 or 3 (a lot!!).
I think you need a safety factor of 3 or 4, and use the full 4500 psi, if thats what you are using. If the regulator fails and applies the full 4500 to your chamber, it needs to be strong enough.
I think you use the tinsile strength , not the yield in the formula.
The downside of this regulator is that it adds extra weight to the gun.
I have “knocked down” that regulator setup so I could do some fall tree rat shooting. Will pick up the project this winter.
I am getting my 9MM gun tuned up for November dear hunting (shhh–dont tell anyone). Ordered some 90 grain hollow point pellets, that should give me 150 FT pounds. A head shot should do the job??
Mark
Reading more about this aluminum it says that because of the copper content it is more susceptible to corrosion than some of the other aluminums. Have you had any problems Mark? Have you finished it in any way?
Looking online at some 2024 aluminum with an O.D. of 1.5″ and a wall thickness of .12″ and using the “Yield Strength” psi of 50,000 since I dont know which to use and it is the lower number this gives me a burst pressure of 8,000 psi.
The operating pressure of this tube will most likely be between 2,000 and 3,000 psi and will be variable between the two. Safe? Unsafe?
Also, Im very curious to see what conclusions you’ve come to as far as required air volume for your regulated chamber. What is nominal to propel the pellet up the tube? What experiments have you conducted or have you only used the tube listed above?
That’s pretty darn cool! I would totally buy something like that. Expecially with that super tight consistancy.
I think you should crank it up and see how fast you can make it shoot. 🙂
Also, being a 4500psi tank and 2000psi regulator, how many shots can you get before you need to refill?
I’d like to see something with a 3000-3500psi tank on the front, so us guys with a pump could fill it up.
Hey Mark, Ive been playing with that Barlow’s Calculator. Its kind of spooky really considering the pressures you are dealing with and I would like to deal with ).
From what I can find that grade of aluminum has what is called an “Ultimate Tensile Strength” psi of 70,000 and a “Yield Strength” psi of 50,000. Which number do you use in the calculator and how much overkill should you use for your operating pressure?
Also, if you are machining your own tubes do you have to be concerned with the tube heating up? Does it change the properties of your material and change the psi ratings? What about anodizing? Do the acids and process change the properties?
Any insight you can offer, or anyone for that matter would be greatly appreciated.
shrpshotr28:
Shot string:
.25 cal, 23″ barrel,
1900 PSI regulated pressure.
31 grain kodiak pellet
the valve, hammer & preload are normally detuned to
about 940 FPS with 3000 PSI
1 907 FPS @2000PSI
2 895 FPS @1900PSI
3 896 FPS @1900PSI
4 896 FPS @1900PSI
5 898 FPS @1900PSI
6 896 FPS @1900PSI
The first one was 100 PSI high, because the regulator
takes about 1 minute to recover the last 100 psi.
I did not wait for the full pressure recovery on shots 2 through 6.
If you look at shots 2 through 6, there is only 3 FPS variation!
It looks like if I kept on shooting the good numbers would continue
till the pressure in the tank dropped below 2000.
Mark
looks really good there mike. Next up, love to see the shot strings on that setup. One of my condor tanks shoots 31gr kodiacs right at 1000fps with only 2300 fill, so will be following this project with great interest.
OK, JUST GOT MY TEST SETUP BUILT.
22 CUBIC INCH TANK IS SHOWN, BUT THE TANK MOUNTING BRACKET
IS BUILT FOR A 45 OR 68 CUBIC INCH 4500 PSI CARBON FIBER TANK.
REAR PRESSURE CHAMBER IS REGULATED TO 2000 PSI.
SO THE GUN WILL SHOOT WITH THE SAME VELOCITY FOR EACH SHOT.
I REARRANGED THE SPRING WASHERS IN THE REGULATOR TO BOOST
THE PRESSURE FROM 1000 TO 2000 PSI.
blue jay:
The chamber is built for 4500 psi, just in case of a regulator failure. Its good for 24000psi burst pressure. The tubing and compression fittings are rated for 7000 psi working pressure, so thats no problem.
If the regulator works ok the normal pressure in the chamber should be 2000 psi (shooting pressure).
Your right about the regulator. I need to figure out a way to pressure test it at about 6000 psi just to be sure.
Your right,, objective #1 –> dont get hurt!
Mark
don’t get me wrong, I like the the direction your running 8)
I did have to re read it though, at first I thought there was 4500 psi at back of the chamber you built which did scare the shit out of me, thats a lot of presser to trust a compression fitting with, but I see that is not the case.
as for the regulator I think I would test it at presser in a plywood box, perhaps two layers of 3/4 just to be safe, better to have a contained explosion, than loose your hand or somethinf worse.
shrpshotr28:
This opens up all sorts of possibilities for stocks. Also the scope could be mounted lower.
A 45 cubic inch carbon fiber tank only weighs 1.6 pounds and has much more capacity than the standard 32 cubic inch AF tank. That will offset some of the additional weight from the air chamber.
theres enough excess material in the air chamber to to allow tapped holes (in exactly the right low stress points) for stock mounting holes.
Mark
looks like the regulated resivoir on the back could be easily made to fit an AR style collapsible stock over it, just an idea.
Blue Jay:
funney, my wife has the same opinion.
The key to this whole thing is the regulator – is it strong enough to handle 2000 psi output pressure?
Just think, a readly available tank, and a cheep regulator.
This could be a kit: the tank could mount to the lower AF rail, the chamber just screws in — then you have a regulated gun.
Mark
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Thank you Mark, I appreciate the reply. I am looking to do something a little different but getting advice from folks who have already tread on the high pressure tube ground really helps allot and saves a ton of time. The point about removing the inside corners is something I wouldnt have thought of and you probably saved me a ton of troubles.