SpudFiles

I want to build a RPG that uses a paintball co2 tank for power. I will be using nerf vortexes as my ammunition. Also, I would like to know how to make it semi-auto, so I can just drop in a rocket, fire, and repeat (not have to worry about opening or closing extra valves). In addition, I would like it to look somewhat close to a real rpg/bazooka/etc. so it will be accepted at milsim events (I will be painting it). I would appreciate any help!

Research coaxial piston valves. You should use a 4" pvc chamber and a 2" pvc barrel, with a modded sprinkler valve pilot. Use a three way valve to pilot the sprinkler and connect the 3 way valve to a regulated CO2 line. This will make it possible to pull the trigger, making the gun fire, then when you let go it the trigger, the gun will automatically fill up and all you have to do it drop a vortex into the barrel then shoot it again.

Thanks for the info, but is it possible to do without the piston concept?

Yes, but I would fear terrible performance. The only other practical thing for your situation I can think of would be just the sprinkler valve as the main valve, with the tank behind and the barrel in front, and a three way valve again. However, this would make it big and bulky, and make it hard to look realistic also. The only good thing about using a sprinkler valve as the main valve would be that you could make a breech load, but I strongly recommend a piston valve, because they are pretty easy to make and the performance we're talking here would be pretty fantastic.

If you could reg the tank town to 400 psi or so, you could have a QEV piloted with a blowgun (or a DCV for the more sophisticated ), with such a light projectile and high pressure you wouldn't need much chamber volume beyond a simple capped fitting.

I am fairly new to all of this, when you post an idea, can you show me a picture/diagram as well? Because I don't really get what you are saying in words, at least until I get all of the terms down.

jackssmirkingrevenge wrote:If you could reg the tank town to 400 psi or so, you could have a QEV piloted with a blowgun (or a DCV for the more sophisticated ), with such a light projectile and high pressure you wouldn't need much chamber volume beyond a simple capped fitting.

Or perhaps a medium chamber and medium pressure?
You could make a coaxial piston valve piloted by a qev, and have a hose that runs from the rear to about 3/4 of the way down the chamber, and add a 3 way valve to that and you have semi auto, but that gives you a gigantic pilot volume and really wouldnt be very good for performance.

Just a question, why does it have to look like a real anti-armor weapon? A made up launcher can look pretty realistic as this launcher.
It looks really simple to make and IMO would be fine in milsim paintball.
From what i can tell, it is just an older type sprinkler valve, pvc chamber/breech loading barrel, a paintball marker trigger, and a regged c02 tank.

That launcher looks fine. I said "somewhat realistic" not one of those with like a 6" pressure chamber and a 2" barrel. However, I would like to model my launcher after the rap4 launcher http://www.rap4.com/paintball/os/bazook ... -4990.html, where the co2 bottle screws into the rear of the launcher. I don't want to have to have a pouch/backpack/etc. to carry the bottle separately.

Here's what the semi-auto valve mechanism could look like using off-the-shelf parts, pretty self explanatory:

OK, could some one give me a parts list and approximate price for the above design?

Chosen_1 wrote:could some one give me a parts list and approximate price for the above design?

That would be spoonfeeding, and the policy on this forum is not to spoonfeed, because if you require that level of help then you probably shouldn't be messing with high pressure. Have a browse through the forums first, the search feature is brilliant if you know how to use it, and I'm confident that all the questions you might have are already answered

jackssmirkingrevenge wrote:Here's what the semi-auto valve mechanism could look like using off-the-shelf parts, pretty self explanatory:

Bah that setup is wasteful. Better off with a slide valve to actually shut off the air supply.

@Chosen_1: The parts are labeled in that diagram... It's just a matter of selecting their sizes and locating them. You have all you need.

Have a look at this, while its not semi auto theres a single 1/4 ball valve you flip to refill. It looks and feels realalistic, while this one uses a piston you could use a sprinkler valve if you want. With Co2 regged down to 100 psi power should be acceptable for paintball with a 1 inch valve. Even if you decide to not use the same valve set up, the asthetics are good.

Can someone give me a link to a how-to-assemble for the coaxial piston type? I couldn't find one in the search.

Here, this one used dwv so replace it with pressure rated parts but should show you the basics of building one http://www.instructables.com/id/A-Coaxi ... ll-Cannon/