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CatgutViolin

One-Day Flamethrower Build

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So, what I intended as a weekend project only took about six hours. Many of you have probably seen videos on making a cheap BB gun out of a soda bottle, since they're all over Youtube, but while this design is marginally more complex to build, it delivers significantly better performance in both rate of fire and muzzle velocity.

 

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Pictured is a 3D printed 'vortex block', the core of a vortex strafer design. I 3D printed it for convenience- it's just a rectangular block with three holes drilled in it. The bottom hole serves as an air inlet, where a push fitting for an air line is routed. The very large hole is the vortex chamber, where the air (theoretically) swirls around, forming a vortex which sucks in BBs and spits them out the third hole (in the upper right of the vortex chamber) through a barrel. I say 'theoretically' since it's not clear whether it actually forms a vortex or not, but it works in either case.

 

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I mounted the vortex block in an iron 1-1/4" coupler, and installed a 12" segment of AEG barrel. I also glued some protective side plates on either side, covering the upper half of the vortex chamber, which prevents BBs from jamming up the chamber when the strafer is full.

 

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The front shows the plastic plate used to seal the front of the vortex block, against a PVC collar inserted into the coupler. This section has to be airtight and able to withstand pressure for the strafer to work.

 

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So, now the actual strafer chamber is attached- it's just a 12" aluminum 1-1/4" Sch40 pipe nipple with a hole drilled in it for a 1/8 NPT fitting. This hole aligns with the air inlet hole on the vortex block, so a fitting for an air line can go through both and deliver air directly into the vortex chamber.

 

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In order to do that, some sort of valve is needed. My teammate used a simple valve screwed directly into the vortex block, but I wanted pistol grip ergonomics, so I used a pressure washer handle with reducer fittings on either end to fit standard paintball/airsoft macroline.

 

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To keep the handle attached, I drilled through two of the screw holes so that they went all the way through the handle, then used a piece of spring steel cut to shape to wrap around the tubing and secure the handle in place. I couldn't put any holes through the tubing itself because it needs to maintain pressure and I can't interfere with the BBs and follower, so figuring out how to secure the handle was probably the most difficult part of the build.

 

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Now properly mounted and connected. At this point, after just three hours of work, with the addition of an endcap to secure the rear of the chamber this would be a fully functional strafer- just hook up the air line to an HPA source, fill the chamber with BBs, screw on an endcap, and go. But I wanted it to actually resemble a flamethrower, and be a little more reliable, so work continued.

 

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The cartridge ignition system on the US M2 and M7 flamethrower wands is distinctive, so I decided to emulate that look for a forend. I screwed a piece of 1-1/2" PVC onto the threads of a second 1-1/4" pipe nipple, and drilled a first ventilation hole. Using a highly advanced engineering technique, I cut a strip of paper to the circumference of the tubing, folded it in half a couple of times, and then marked the folds with lines. I then taped this to the tubing to serve as a guide.

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Which gave me evenly spaced ventilation holes. Pretty easy. A couple of slip fittings finished up the nozzle.

 

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Now, the spring follower. Strictly speaking a vortex strafer doesn't need any kind of follower to function, but unless the hopper is above the vortex chamber, it won't be able to fire if you aim upwards as the BBs roll to the back of the chamber. So, this follower, made from ABS cut into a disk, a homemade wire spring, and the cap from an epoxy putty tube, pushes the BBs towards the chamber regardless of orientation. The problem I quickly noticed was that with the chamber nearly full, it was extremely difficult to stuff the spring into the receiver without it tangling.

 

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So, a redesign. Same ABS disk and cap, but now an aligning rod made from a piece of brass coat hanger wire, and a smaller spring from my toolbox. This is much easier to stuff into a full chamber.

 

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To complete the wand, I used pipe straps to attach an empty MAPP gas bottle and a screw-on torch. Logically this makes no sense since a cartridge ignition system (as the forend is based on) doesn't require a torch, but everyone I asked said it looks more like a flamethrower with this so I'm not going to argue. It's all for show so if it looks better this way, so be it.

 

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So, now the tank- because a proper flamethrower needs a big, obvious tank that screams 'I'm the biggest threat, shoot me first'. This is a 3 gallon air tank, bolted to an ABS stabilizing plate, bolted to an ALICE frame. Notice also that an ALICE shelf has been attached to the bottom of the frame.

 

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The shelf allows the real air tank, a standard HPA bottle, to sit on the frame and be secured in place via an ALICE tiedown. The combination of a smaller and larger tank mimics the arrangement of real flamethrowers, which use a small gas bottle to pressurize a much larger fuel tank.

 

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A fuel hose links the fake air tank to the wand, and the real air line is snaked all the way through the fake hose, through the air tank, out the top, and over to the HPA bottle. I still need to paint the whole thing, but it is functionally complete.

 

Here's a quick overview video, including test firing at 0:40. It appears to be shooting around 100rps, and while I can't get a good reading on the muzzle velocity, it should be significantly higher than the 200fps my teammate's does at the same pressure (thanks to a longer, narrower barrel and smaller chamber).

 

Edited by CatgutViolin
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Very cool.  Have you done any range testing? 

 

Just imagine turning a corner in a CQB environment and being hit by a wall of BBs from that heh.

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Very cool.  Have you done any range testing? 

 

Just imagine turning a corner in a CQB environment and being hit by a wall of BBs from that heh.

 

On prior designs, the range generally tops out at around eighty feet depending on ammo and pressure, but our newer ones like this use much smaller chambers which dramatically increases their efficiency, so we're expecting better. Most CQB fields I've played at are semi-only, so the niche for a device like this is actually outdoor games where there's enough cover to get reasonably close, like MOUT or woodlands.

 

It's really just a matter of surviving long enough to get good positioning. Then it wipes out squads.

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Mmmm, I'll have to be the fly in your soup and ask you: aren't you afraid you'll get overkill complaints?

Ricochets usually don't count in airsoft, while it's seems to be the very tactic for flamethrower cqb.

 

If you'd go with high rpm, I'd lower your fps dramatically and not use a hop system ( dunno if you planned a hop).

 

Kudos on the project as a whole though, I like being a flamer on Day of Infamy pcgame ^^.

 

Sent from my C6603 using Tapatalk

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I actually built one of these a while ago that works pretty well off of an air compressor, but I've yet to hook it to an HPA tank. How much firing time does your tank get you?

 

I haven't used mine in-game yet, but on prior designs, a 68/4500 was enough to get through most of a day of play. This 62/3000 won't be enough, but that's why I have a scuba tank fill station to lug to the staging area and refill as needed (and by 'as needed', I mean 'at every opportunity'). These things suck down gas like nobody's business. With HPA, being able to refill at the field is basically a necessity.

 

My teammate who pioneered our designs originally used a large CO2 tank (you can see it here), and that had more than enough gas for a day of play, but cooldown was a significant issue.

 

Mmmm, I'll have to be the fly in your soup and ask you: aren't you afraid you'll get overkill complaints?

Ricochets usually don't count in airsoft, while it's seems to be the very tactic for flamethrower cqb.

 

If you'd go with high rpm, I'd lower your fps dramatically and not use a hop system ( dunno if you planned a hop).

 

Kudos on the project as a whole though, I like being a flamer on Day of Infamy pcgame ^^.

 

Sent from my C6603 using Tapatalk

It sounds like it functions as a flamethrower should, a close range terror weapon. Providing the FPS wasn't too high I'd happily go to a game that involved this as it would add an interesting, and stress inducing dynamic to things.

 

Totally legitimate question on the muzzle velocity, and one we're very cognizant of. Being allowed to run our abnormal equipment is entirely contingent on not pissing off everyone we play against.

 

This one, with a higher muzzle velocity by design than our previous models, does around 275fps and 100rps @ 110 PSI as demonstrated in the video. Normally we have them doing ~200fps, so I intend to drop the pressure to 90 PSI or so, which will also reduce rate of fire and therefore ammo consumption. And yes, we've discussed hop-up and a fixed hop would be easy to build, but we decided it's simpler and more thematically appropriate not to use one. Even with a low muzzle velocity it's not hard to get 75+ft just by arcing, which works a lot better at 100rps than with a typical AEG. Not using hop-up with a low muzzle velocity provides a significant, quantifiable disadvantage that helps us get approved even at fields that normally have rate of fire limits.

 

For outdoor, woodland-type games we commonly use .2s, and at a ~200fps muzzle velocity a .2 has basically no energy by 30-50ft out. For games in more built-up MOUT-type environments we use .12s, which in addition to going absolutely everywhere in-flight have negligible impact even from point-blank range.

 

We've asked players after our games what it was like going up against it. The general consensus is that it's like getting a handful of BBs thrown forcefully at you, alarming but not painful, and nothing like getting stitched up by a 400fps P* running 50rps.

 

And yes, it's unfortunate for verisimilitude that ricochets don't count. But generally speaking, even without ricochets, it's very good at flushing people out of cover. It doesn't matter how little of a target is exposed, if there is anything visible it will get hit by at least 1 BB.

Edited by CatgutViolin
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Man, did I really build this thing a year ago? Time flies. Anyways, I did a video with Novritsch back in October, and it looks like he just uploaded it. Figured I'd post here to keep it all in one place.

 

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