Legal warning Please note that the specific details of this project's construction have not been replicated online, nor will be made available at any point. Do not email the author or hosting site asking for further information as none will be forthcoming.

This project was built in the USA where such pneumatic rebuild constructions are perfectly legal. The intention of this project was to project a foam marker safely for wargame simulation purposes. No other purpose or intention should be construed or implied.

This project is posted here for information and entertainment purposes only. United Kingdom residents should note that it is against the law to attempt to reactive spent munitions tubes (such as used AT4s) for any purpose.

Background I can't remember where the whole concept started, but back in 2002 one of the players in Ohio showed off a home-built RPG that operates off a ball-valve and shoots foam warheads. Although it was grossly inaccurate, I thought that was fun and most importantly, if someone can build that, I can build one better. Fast forward to today, I have my airsoft AT-4 sitting in my living room waiting for the world to see it.

Authenticity I think one of the major difference that set this one aside from other (former) airsoft AT-4 is the fact that it being 100% authentic, both in appearance and control. It looks identical to the army's AT-4 because it is built on a de-milled AT-4 tube. It uses 100% of the original switches and buttons and even safety of the military's AT-4. It is also a fully mechanical design which does not require any power source to fire (nothing to fail you).

Besides the weight (or if someone is dumb enough to look directly down the tube), there is no way you can tell this is not the real deal. For example Florida Airsoft has their own version built earlier this year using an electronic sprinkler valve. However to accommodate the valve, a hole has to be cut in the AT-4 and they have to build a small box to cover the sprinkler valve that sticks out of the AT-4 tube. It works great, but I personally think there is two drawbacks:

1) the external box obviously detracted from the realism aspect, but more importantly
2) a electronic sprinkler valve requires batteries to operate and it won't work if the battery has been drained for whatever reason.

Performance Ok then you may ask, how far does it shoot? Is it lame? Well that depends on how you look at it and what you compare it to. With the prototype we were able to send the Nerf football over 100 meters away (300+ feet), with the ability to accurately hit a vehicle at 40 meters (130ft). Due to the limited space inside the AT-4 (and hence shorter barrel) the range is somewhat reduced, as we've found that the flight path becomes very unstable at higher velocity. Regardless, if you compare it to the real-steel AT-4's spec, its pretty lame. But as an airsoft "bunker buster" or when used in scenario games to destroy "vehicles" or "structures", it can be very effective.

Thumbnail shots above link to a video of project in action. Video requires DivX to play, and is 1.4Mb in size.

In addition, the concept does not limit its use to only fire Nerf footballs. Due to the modular design you can attach any size barrels (up to 84mm O.D.) to the unit, which means, for example, it can also shoot hundreds (if not thousands) of BBs all at once using a sabot round for a major shotgun effect. One of my earlier version shot a Mickey-D chicken finger at god-know-how-fast. It can also adopt to fire a single paintball round if the scenario calls for (i.e. marker round, to identify a "vehicle" has been "destroyed"), smaller Nerf footballs (for increased range), tennis ball (cheap alternative ammo), or anything that you can fit inside a 84mm tube.

How does it work? Well, first and foremost, I will tell you that it is basically a very specialized pneumatic (not hair-spray or propane based) spud gun sleeved inside an AT-4. Secondly, I will also tell you that I will not share the details for obvious reasons (i.e. people blowing themselves up). Two people were KILLED earlier this year in Marysville, Ohio when their spud gun exploded, with many observers seriously injured. They weren't ignorant kids not knowing what they are doing (they were ignorant adults who didn't know what they are doing). So do yourself a favour, unless "you know your stuff", don't try it. And please don't ask, neither the AT-4 itself nor any of the building schematics, parts lists, or plans will be made available for sale.

That being said, what I can tell you is that the inside unit, as pictured, are mostly PVC parts with a heavily modified pneumatic-actuated piston design. If you search online for spud gun or potato guns you will eventually come across piston designs. However unlike most designs you may find, my piston is actually located in FRONT of the unit due to the unique requirement of the large bore barrel and limited space inside an AT-4 (most of the online plans show a rear-piston design). (Update: The latest version went back to a rear-piston design for serviceability.)

In operation, pressurized air is pumped via a valve into the pressure chamber (the very large, 30-inch long portion that makes up the rear part of the spud gun), up to your preferred pressure. I have tested the unit up to 120psi (that's as high my pump will go), but at 120psi the pressure coming out of the delivery tube was so strong that the outgoing air will literally rip the mini-football's tail fins off, sending them out with no rear-stabilization while they tumbled to their death. Nonetheless, the weakest PVC component in the mix is rated at 250psi, with the metal valve rated at 150psi so I have a fairly high safety margin - not to mention the whole thing goes inside the fiber-reinforced AT-4 tube that could withstand the heat and pressure from a real rocket’s engine. After the pressure chamber is pressurized, your warhead of choice is loaded from the front.

When the time to fire comes, the operator will pull the safety pin, move the cocking handle from "safe" to "fire", depress the safety switch, then press the fire key - 100% identical to a real AT-4. (You can even open the sights if you really wanted to.) At that point, the modified original AT-4 firing pin will strike and open a small pressure relieve valve that actuates the piston and allow the air to move from the pressure chamber to the barrel, hence firing the projectile. There is provision for the weapon to be "field-reloadable" by using 12g CO2 cartridges, however for realism I'd prefer the operator take the AT-4 back to staging area and reload there, since the real-deal is not field-reloadable either.

Cost Finally, you may ask... how much would it cost to build one myself? So here is the figure. The de-milled AT-4 tube cost me $400 shipped, and they are getting rarer every day so expect the price to go further up. I've been searching for 2 years and I have only been able to find two (update: Just found another 3 units at slightly under $400 each, but I’ve recently heard reports of $200 units).

The internal components (PVC pipes etc.) cost about $150 (cost of parts only, time involved in designing and machining the parts are not included). So the material for this particular unit is right around $550. Now I have to also mention that, for me (which is relatively dumb) to get it to work, I am now at my 7th version spud gun design. Each prior version cost anywhere between $80-$150 in material to built, so I have yet another $600+ wrapped up in non-salvageable parts (R&D cost?).

All told I've dumped well over $1000 into this project, plus countless hours of "why the hell does it not work?" during the past year (yes I got my first AT-4 tube at least a year ago and I've only just got it to work - shame on me). I am sure there are smarter people out there that can get it done quicker and cheaper, but the bottom line is that since the AT-4 tube itself is so expensive, it will never be "cheap".

Conclusion I hope this project will spark other's creativity in coming up with additional "alternative" safe simulation weapons for future Airsoft scenario games – mortars, artillery simulators (already in the work… hehehe), claymores, land mines… except alien rifles (j/k). Although it is very true that "everything is possible, it just has a cost", I hope there are others who are as determined and as dedicated to make airsoft a better sport. Let the fun begin!

Ez.Wallace