Need help with SMAW styled launcher

[Berkut]

First, a little background: I recently attended Oklahoma Invasion 6, a very large MILSIM airsoft operation. My squad and I were advancing along a road with a friendly SpecOps fireteam. We get orders to reroute to a different position and as we leave, we warn the SpecOps squad about an APC rolling on their position. A little while later, we go past a group of enemies bleeding out and talking about how some SpecOps guys ambushed them with a couple AT weapons.

The thought of having that much firepower made me want to be our squad's AT gunner, so I began to hatch ideas for one and thought about the SMAW launcher. I have a significant portion thought up, but I am having a hard time coming up with an idea to connect the trigger to the valve in the removable rocket casing in an effective way. I plan to use 4" belled end pvc pipe for the outer body, and 3" belled end pvc pipe for the chamber and barrel. I want to be able to attach the rocket shell and fire without having to fumble with connecting anything on the inside of it.
Is this a possibility, or am I thinking to large?

[jackssmirkingrevenge]

Are combustion launchers allowed? It would provide sufficient power for your purposes while greatly simplifying contruction and allowing for the possibility of rapidly reloadable shells.

[Berkut]

I had thought about a combustion type launcher that connected a sparker assembly built into the rocket casing to a battery and trigger switch in the grip via contacts. I sent an e-mail to one of the admins about it and I should have a reply by tomorrow, although unfortunately my first guess is no.

[jackssmirkingrevenge]

Shame, having preloaded combustion cartridges along these lines would be a very easy way to go about it, and if you use a small combustion chamber they would be perfectly safe.

Making preloaded pneumatic cartridges is a slightly different matter, and it greatly depends on what materials and tools you have to hand as to whether you can make it work and realistic at the same time.

One option could be having a small HPA bottle in the grip with a 400 psi or so output, trigger would be a blowgun and cartridges would have a burst disk or friction breech so they would simply have to be closed tubes with some perforations for air, conceptually like this.

Another idea would be to have the propelling air as part of the projectile but if you're stuck with those nerf rockets then it's a non-starter.

[Berkut]

I actually saw the first thing you linked while I was lurking before I signed up and would have used a variation of that.

One option could be having a small HPA bottle in the grip with a 400 psi or so output, trigger would be a blowgun and cartridges would have a burst disk or friction breech so they would simply have to be closed tubes with some perforations for air, conceptually like this..

Just to make sure I am understanding this correctly, this would require moving the chamber forward to be more above the grip than behind the shoulder, correct?

[jackssmirkingrevenge]

Just to make sure I am understanding this correctly, this would require moving the chamber forward to be more above the grip than behind the shoulder, correct?

Not necessarily, I attached a diagram of what I had in mind. It needs a reasonably airtight seal on the cartridge in order to allow an overpressure to pop the projectile like a champagne cork.

You could either have the cartridge lock in place, or be blown out on firing. The latter will decrease reload time but will be to the additional peril of whoever is standing behind you...

[Berkut]

Locking it into place would be best from a realism standpoint as well as a safety standpoint, as the real SMAW rocket casings require a clockwise turn when loading.

In your design,would the tank be good for multiple uses?

[jackssmirkingrevenge]

In your design,would the tank be good for multiple uses?

Do you have access to paintball tanks and filling equipment?

A 13 cubic inch tank is compact enough to fit your project and will give you enough shots to last a game (3000 psi regged down to 400) - you can design it to use very little air per shot.

[Berkut]

No, not regularly at least.

I would like for the casings to have a fairly self-contained propulsion system. perhaps the casings could be pre-pressurized and the tank would push the pressure over a burst disk's threshold like in the attached image?

[Crna Legija]

No, not regularly at least.

I would like for the casings to have a fairly self-contained propulsion system. perhaps the casings could be pre-pressurized and the tank would push the pressure over a burst disk's threshold like in the attached image?

you could use a trigged burst disk

[Berkut]

I like the idea of the triggered burst disk. An electrical trigger for the burst disk would be perfect for this launcher. I looked into the resistance heating wire the spudding handbook talked about, but I would like to avoid ordering it online. Is there a better alternative, or at least somewhere to look locally for some? Has anyone tried the wire burst trigger set up?

[jackssmirkingrevenge]

Has anyone tried the wire burst trigger set up?

I had tried it a long time ago (sadly the image link is dead) and it worked pretty well, basically I used mylar tracing paper as disk material, holds pressure well and fails consistently when heat is applied.

A good source of wire is an old heat gun or hair dryer, there's tons of suitable nichrome wire inside.

There are several other ways of making self contained cartridges using a variety of valves, it depends what resources you have to hand in terms of materials, tools, time and money.

Have you confirmed that combustions are out by the way? With a simple 1x combustion you have the advantage of not needing a pressurised mix in the cartridge.

[Berkut]

Yeah, just got a reply from the admin. nothing combustible. so that leaves pressurized air.

In the wire burst disk, does the wire break when the disk ruptures? and at approximately what psi does mylar rupture?

I used trial and error in GGDT to approximate the minimum PSI for my barrel to about 87 PSI. Here are GGDT screens at 87 PSI, 100 PSI, and 150 PSI.

Unfortunately right now, I am not at home where my sketchup file is, so I had to modify one of the images I uploaded using paint. It isn't great, but it gets the point across.

[saefroch]

In the wire burst disk, does the wire break when the disk ruptures? and at approximately what psi does mylar rupture?

I would expect that the wire does not break, but it may so I'd be ready to replace it if it does. The mylar will rupture at a different pressure depending on how large the disc is. Just try it and find out, I suggest.

[jackssmirkingrevenge]

In the wire burst disk, does the wire break when the disk ruptures? and at approximately what psi does mylar rupture?

In my experience, unless you overload it, the wire won't break. The bursting pressure depends on the diameter exposed to pressure.

After a brief rummage in the scrap box, I managed to dig up my prototype. Note how I inletted two brass tubes to make the wire replaceable.