My first air cannon. Going to be used to shoot nerf balls :]

[Jarrado]

So far I have the following in the picture to work with. A QEV4 I picked up, a co2 charger that has a co2 regulator I can use till I get a palmer, a remote line, 20oz tank, 4 co2 12g adapters.

Im trying to keep it all inline for aesthetics and want as loud a "pop" as I can get without spending much more, with the exception of the palmer. Which, if someone has a palmer for a tank they would sell, I'd appreciate it.

Im going to be working on about 80-90psi and will install a 125 psi blow valve in my steel expansion tank behind the barrel. I think I'll be using regular galvanized steel. Probly 2''x12'' long. plus adapters. Then a 18'' pvc barrel fitted for nerf rounds.

Im trying to source a decent 3 way valve that wont come from china /: that isnt super expensive. Havent had much luck. But do I really need one to vent the QEV? I want it to have a "trigger" mech, so ball valves are out, but since Im using the QEV as my main valve, I figured that anything else would pilot too slow.

I'll also use this during large airsoft skirmishes as an anti tank weapon. So I plan on wrapping it in up and painting it to look like an AT4 or maybe a swiss gustav.

I understand enough to know which way the air flow is in relation to my QEV. Air>ball valve>Expansion chamber>QEV (3way,pilot)>barrel>exit. Gotta start somewhere though. haha.

The 12g's are for simple straight line launchers.... just gonna slap spring loaded ball valves on em. I'll fab them myself. Pull, lock, spring open.

I'll also be making two different sized barrels. 40mm~ and 52mm~ or whatever is closest to my ammo Im using. Still have to go check. I'll be using pressure rated pvc sch 40. Maybe sch80 if I can source any.

Pictures of the parts I have so far, I'll post up as I go along.

http://i116.photobucket.com/albums/o24/ ... _01761.jpg

[Just1ofgod]

do you think the steel barrel might be over kill for shooting nerf balls how fast do you want those things to go??? at anyrate looking forward to seeing the results and i dont know alot about three way valves but im sure JSR will be along to tell us how it should be done

[Jarrado]

Yea. Im trying to see if If I can find a cheap pilot option for my QEV4. Not looking to use a sprinkler valve.... to bulky.... Might have to order a 1/4 QEV and wait the 2 weeks it would take to get here. /:

My QEV4 is made by Humphrey 3/4" Does anyone know the highest pressure used on one of these? I see it says 120psi rated on the side, but I've seen people taking these to 300psi on spudfiles, so I thought I would ask. Couldnt find any threads on this.

Im also not sure what size barrel I could push with my 2''x12'' chamber. I think Maybe the chamber is too big. Maybe I should change it to 3/4"? I read that higher volume means I can use lower pressure? Or should I go with 90psi but lower volume? Sorta confusing.

EDIT: Found it. I have a shuttle type. So it SHOULD be able to handle pressure up to 300psi. But I will not go above 120psi.

[Just1ofgod]

yeah im no expert on qevs by anymeans i understand how they work but i have not used them much how ever i can say that if you run a higher volume you can get alot more performance out of lower pressure just make sure you have as little restriction of flow as possible ie running a bigger qev also of course longer barrel will help as well hope this helps looking forward to seeing it when your done

[jackssmirkingrevenge]

Im also not sure what size barrel I could push with my 2''x12'' chamber. I think Maybe the chamber is too big. Maybe I should change it to 3/4"? I read that higher volume means I can use lower pressure? Or should I go with 90psi but lower volume? Sorta confusing.

At 90-100 psi, assuming you're using nerf "vortex" type projectiles, 2" by 6" should be enough for decent performance. 40mm will definitely not work as those rounds are just over 50mm, they can be squished of course but not that much

You don't need a very long barrel either, for that chamber volume 12" of barrel length is probably almost too much.

Im trying to source a decent 3 way valve that wont come from china /: that isnt super expensive.

I don't see all those factors coming together. Nothing wrong with Chinese ebay stuff to be honest, all the parts I've used so far have been reliable and of good quality manufacture.

[Jarrado]

Im going to use a blower valve for now and order a 3way off ebay. Just have to wait I guess.

Im going to make a screw on barrel so I can change chamber sizes. Seems like a good option since it will be wrapped in the center for support anyway.

So, your saying a 2"x6" expansion chamber to a 12'' barrel is more than enough? So overall length would be somewhere around 2ft.

As far as ammo.... I'll be trying a few different kinds, some just for gags. Teddy bear launches. lol. Mainly going to stick with vortex, mini vortex and homemade canisters for indirect fire. Maybe use rolled up socks lathered in talcum powder. Still working on it.

Question. Would cellular PVC be ok for the barrel only? Not expansion, for that I'll be using some galvanized steel, which will be sandblasted and cleaned prior to assembly.

[Just1ofgod]

i have run PVC up to 200 psi without any problems much past that i dont know how safe it would be as long as your not using cheap PVC it should be fine for what your using it for

[MrCrowley]

Would cellular PVC be ok for the barrel only? Not expansion, for that I'll be using some galvanized steel, which will be sandblasted and cleaned prior to assembly.

It's probably ok for a cannon running 90-120PSI shooting only mini-nerf footballs from a 50mm PVC barrel (the nerf football should be a fairly loose fit, if it needs to be jammed in then a cell core barrel isn't such a good idea) but I wouldn't recommend it.

First of all, it's way less fun shooting a cannon when you're worried about one of the parts failing; especially if that part may fail dramatically and send shrapnel everywhere. Second, if you're using this for airsoft skirmishes you probably want it as safe as possible as other people have to trust that you've built this cannon correctly. Bottom line: don't cut corners, it's not worth it for only a few dollars.

If you want to use cellular PVC because it is a better fit for nerf balls than pressure rated PVC, I would suggest that you explore some other materials such as aluminium, copper or ABS. If that doesn't work out, see if you can sleeve the cellular PVC with another piece of pipe (members in the U.S. commonly sleeve non-pressure rated SDR-21 pipe that fits golf balls with pressure-rated 2" Sch80 pipe to make it safer) or wrap it in fibreglass.

I know PVC internal diameters differ between Aus/NZ and the U.S. so I can't guarantee that your 2"(50mm) pressure rated PVC will have the same I.D. and fit nerf balls but I'm sure it's close enough.

Have a read of this:
http://www.spudfiles.com/spud_wiki/inde ... sure_rated

Even though 2" PVC is rated for above 200PSI in some cases, I wouldn't recommend that you ever take PVC that size above 130PSI. Some members have done so (perhaps Just1ofgod has done this but his post is dangerously vague as it makes no mention of the type of PVC or its diameter), but I would recommend pressure rated ABS or a metal for 2" diameter high pressure cannons.

[Jarrado]

Just read that, I may order some sch120 or 80 PW from a local supplier just to be safe.

Its looking like I can also make them very light and compact, which is most excellent considering these will most likely be used in woods with much walking involved.

I see some players here have launchers with barrels that are over 18" in length. So a shorter barrel will actually yield higher long distance accuracy?

At this point safety>reliability>ease of use>accuracy>distance>power.

Thanks for the advice as of now and for having patience with me till I learn to find the needed info on this forum. Not a fan of "spoon feeding" myself.

EDIT: I thought I should mention, Im looking for this too "auto fill"-or for the QEV to close if the air is left on-co2 after a shot. I understand that my QEV will allow this if it is filled from the "IN" side? Im also trying to get about 300 foot max range.

[Jarrado]

Could I use something like this to pilot my QEV?

http://www.ebay.com/itm/PNEUMADYNE-A11- ... 2576222d27

EDIT: Ahaha.... found out I also need to be able to shoot 87mm rounds.... dang. Ok..... that means a way bigger barrel.... and I'll have to extend the whole system some for added volume. I'll stick with the ratio you told me and increase the barrel length to about 18". I think I'll make separate launchers for my 52mm rounds and abandon the idea of "switchable" barrels. Im thinking about making the barrels out of thinwall steel. I have a welder to weld fittings on. Might be cheaper. SCH40 PW is about $25 a stick here.

[jackssmirkingrevenge]

Could I use something like this to pilot my QEV?

Yes, but given the calibres you're contemplating, maybe a small QEV is not the best valve for the job.

[Jarrado]

Hmm...... Well. I have the QEV, so I can use it to make the 52mm for the small ammo.

EDIT: Tested it out and realized that a full size nerf rocket could cause injury. So 87mm is out the window. Sticking to the smaller ammo.

EDIT2: found 15ft of 2'' sch80 in the back of my shed, so Im good for barrels now. Bought a palmer reg that was on clearance, so I'll be using that instead of the madbull 12g reg.

I looked up ratios for barrel to chamber and its just super confusing. I need the overall length of this larger launcher to be 3ft or so, since it will be going into a gustav shell. I read that 1:1 is a good ratio to start with, but Im thinking 1.5:1, so I can use lower pressures, then I can turn the psi up to shoot slightly heavier canister rounds?

[Jarrado]

Ok. Got my parts in. Now just to figure out what the final length will be, get fitting, etc. I realize I have the QEV backwards in the photo, I'll have the exhaust side facing the proper direction when I go get fittings.

Couple of questions:

Can I simply drill and tap the 2" expansion chamber and screw in a safety blow valve? Or do I need to use some kinda tee fitting? I do machining, so making a proper threaded hole is peach easy.

Im looking into making this a breech loader, but how would accuracy be impacted if the ammo is loaded breech or end loaded not being pushed down with a ram rod?

And ratio. Should I just make a 2" chamber 16" long for a 16" barrel? I keep reading conflicting opinions all over the web. I would really NOT want to take this apart after its done. I also read that some people use as much as a 2:1 chamber/barrel ratio. 0_0

Im looking to keep the actual PSI as low as possible, since I want my rocket ammo to stay intact for as many shots as I can.

[Lockednloaded]

Sorry, but you have that QEV setup completely wrong in your sketch. You have your barrel hooked up to the port for the pilot, you have your pilot hooked up to the port for the chamber, and you have your chamber hooked up to the port for the barrel

[Jarrado]

Yea. I did note that in my post. I just tossed it down for a quick picture.

And I thought the EXH side was the side that needs to hook to the barrel?