SpudFiles

This is a metal burst disk gun that I have been working on for a while, because it had so many bugs. It is now very consistent, working at least 95% of the time. The name is a parody of Gort's QCTBDC, and stands for Slow Change Triggered Burst Disk Cannon, because it can take 10 minutes to reload. The noise and destruction caused when it fires is certainly worth the wait though (yet it's not quite as loud as I've been led to believe that a BD cannon of this size should be- maybe my hearing has just been dulled by listening to my iPod too much)
Without further adieu, here are the specs:
Chamber Volume- ~100 cubic inches
Barrels- 1.5"x24"
- 0.75x72"
Valve- triggered burst disk, 1.5" porting
Range at 160 psi- no idea
Velocity of 5 gram round(20 airsoft rounds) in .75" barrel at 160 psi- ~1000fps
Velocity of 210 gram penetrating ammo (saboted iron dart) in 1.5" barrel at 160psi- ~245fps (433 foot pounds of force)
Misc.- This launcher is built entirely out of galvanised steel and brass fittings. The highest pressure that I have taken it to is 160psi. I tried to take it higher, but the gauge on my Crappy Tire bike pump exploded (when they say 160psi max pressure they mean it). My usual ammo is the aforementioned saboted iron dart which I will include pictures of, and my main target is an old computer that I got from my school. The recoil when firing the dart is tremendous. I don't know how 433 foot pounds compares to normal firearms, but judging by the carnage it inflicts on its target, and the way the 15-20 pound computer is thrown at least 3 feet back (as I can prove with a video), it is quite powerful. I haven't tested how much plywood this dart can penetrate, but it made a clean hole in 3/4" plywood and kept going. I plan on taking it to as high pressure as I can reasonably get to (hopefully 250psi), but I need a disk that can survive about 150psi in a 1.5" union if I am to do that. I usually use disks that are made of 16 layers of alu. foil, and pressurise the secondary chamber to 80psi, and the main chamber to 160.
Here are some pictures of the gun, its ammo, and the damage I have done so far (mostly to the computer)

This video is a chronicle of the development of the SCTBDC-100 from its first shot to its present state.[youtube][/youtube] ...see 250 psi copper riffle for rest

oh cool a 2 burst disk activation, I think it needs a larger chammber, there should be more of these in the spuding world

how does it work

The current chamber gives it a 2:1 CB ratio. I can't make the chamber wider, because 2" is the biggest size that I can get galvanised steel in, and pressure rated PVC isn't available here. The chamber could be longer, but I have to pump this with a bike pump, and it already takes quite a while to get to 160psi. I may be able to increase the pressure though, and that would definately help with having a small chamber.
EDIT: look in the wiki at Triggered Burst Disk to see how it works. I don't feel like explaining and you could have searched to find out.

Looks great, nothing like the raw power of a burst disk and high pressure.

Since you are using high pressure and a hand pump I would suggest doubling the barrel length to 48" and cutting down the chamber to 24" if not more. That will make less pumping for you and still give you better performance than you currently have.

433 foot pounds is definitely comparable to firearms, a .22 rifle has a muzzle energy of around 110 foot pounds (I think, someone correct me if I am wrong).

I don't mind pumping the chamber as it is, I just don't want it too much bigger. Clide: I already have an old 1.5" ABS barrel that's 4 feet long. I should be able to get 300fps and 679 foot pounds of force with that. Thanks.
I will likely update if I am able to get it to 250psi (and survive). At that pressure GGDT says that it should get ~370fps and >1000 foot pounds of force (don't know what kind of firearm that will compare to)
Any ideas for a burst disk material that would fail at ~200psi in a 1.5" union?

pressure rated PVC isn't available here

wow that sucks,
in case some of you don't know and for Lucky this is actully a 2burstdisk gun, that goes off when you want, because there is a little bit of presurebetwwen the burst disk, the presure helps support the first disk from bursting, so when the presure is gone the burst disk loses suport from the presure and breaks the second disk is a much lower presure disk just enogh for the support presure and is esailly broken

You might try some plastic signs(a little expensive, but they break well and are pretty consistent) or multiple layers of some plastic disposable plates. Or you could try some thicker aluminum like maybe some cut up aluminum cans.

Wow, very nice cannon. I really like the power of burst disks, which you have got. Well done! A real beauty

looking good, shame about the short barrel for the 1.5" as I'm sure the energy potential is much higher. How about another elbow and having it in over-under configuration, that way you could maximise the barrel length while keeping overall dimensions manageable.

Nice cannon. It's nice to see a few more people experimenting with the actuated burst disk design. Gives me hope that, just because mine failed to work right, the design is still good. 8)

If I were to make another one, (which I'm not because I'm out of spare money), I'd try Sgort's idea. Just because I'm better at sealing off moving components than making simple things work.

I tried a 4 foot 1.5" barrel today, it worked far better. I fired it at a drive bay area, and it shot through at least five layers of sheet metal and embedded the ammo almost all the way in. I may make it an over under design, but it still wouldn't be exactly portable due to the amount of setup and long reloading time. I didn't really mean this to be portable in the first place, it is designed for sheer power, hence the choice of the inline configuration and burst disk valve. I had a VERY hard time getting this to work, but it worked 100% of the time after I fixed it and got it to seal properly. Still haven't shot through that computer though. Maybe if I can get it to 250...
EDIT: What kind of plastic signs do you mean? I have tried aluminum cans before, but they seem to tear and break at about 40psi in a 1inch union.

Like plastic signs they would sell at a hardware store. For sale, beware of dog, no trespassing, etc. Three layers of those held back 120 psi in a 2" union, so it might be able to do 200 in a 1.5"

Thanks, I'll try that. The 10' barrel will be coming soon. That, and 200psi, should go through the computer (GGDT is giving a velocity of 423fps and a muzzle energy of 1285 foot pounds of force with this setup.)