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200psi metal cannon Update:lots of damage pics

Built a pneumatic cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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Unread postAuthor: DYI » Mon Jan 28, 2008 7:34 pm

i made this a year ago and just today realised its potential to be the next SCTBDC


You've got a little ways to go yet. The armor piercing broomstick is a good start though (find a thread called "Carnage" if you don't know what I'm talking about).

Im also on a low budget (8-13 bucks a week)


Well, at that rate you could build a whole SCTBDC, complete with R&D in ~1 - 1.7 years :P Ever thought of getting a job? You'll thank yourself in the long run.
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Unread postAuthor: bigbob12345 » Mon Jan 28, 2008 8:52 pm

I realize this does have a ways to go before it becomes a SCTBDC but I am thinking maybe 2ft of 1.5in steel pipe to finish it off. I dont really need something as big as the SCTBDC but this would be my most powerful pnumatic yet. I would get a job but the thing is im 14 :lol:
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Unread postAuthor: DYI » Mon Jan 28, 2008 9:07 pm

I was 14 when I got a part time job at a pharmacy. Believe me, it's amazing what you can do with $60/week.

And I don't need anything the size of the SCTBDC either, it just started growing, and I couldn't stop it :roll: Believe it or not, the SCTBDC was actually a handheld design in it's first incarnation.
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Unread postAuthor: bigbob12345 » Mon Jan 28, 2008 9:15 pm

60 bucks a week would be nice
I had a look at that carnage thread you were talking about and those where at 160psi right.I have to pump this thing up with a bike pump currently but soon i will use dry ice in all my metal guns.I like how its so Quick to pump up but gets almost equal power to this.
http://www.spudfiles.com/forums/my-most ... 12468.html
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Unread postAuthor: DYI » Mon Jan 28, 2008 9:24 pm

From my experiments with the HPHH (in pneumatic showcase), with a ball valve, you either need a longer barrel or a faster valve a lot more than you need more pressure. The only advantage that 500 psi has over 250 in a ball valve gun is a louder bang, and more pissed off neighbours wondering what just blew up.

With a fast valve like a burst disk, increasing pressure has an extremely beneficial effect on performance, even 50 psi or so. The difference in the SCTBDC between 160 and 500 psi is a factor of almost 5, while the performance difference between 160 and 500 psi in the HPHH is a factor of less than 2.
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Unread postAuthor: bigbob12345 » Mon Jan 28, 2008 9:34 pm

Yea Im going to get a union so I can use burst disks and my neighbors are surprisingly tolorant they have only complained once and that was a really really load bang(accedintal explosion of a pop bottle)And they have never called the police.And Im surprised that in the SCTBDC tripling the pressure increases performance so much I would of thought it wouldnt make that margin of difference with a fixed barrel size. Thats good to know it will help with upcomeing projects.
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Unread postAuthor: DYI » Mon Jan 28, 2008 9:50 pm

My neighbours are exceptionally tolerant, but the SCTBDC is also exceptionally efficient. You can barely even hear it a block away. My neighbours usually don't even notice when I fire it. It defies most people's expectations of how loud a 500 psi, 3" bore burst disk gun should be. Apparently, it transfers ~85% of the potential energy in the chamber to the projectile.

On the other end of the scale, the Oxy/MAPP hybrid that blew up in my face was apparently heard throughout the entire town to some extent... I was probably the only one that didn't hear it. I tapped two wires together, registered a massive shock to my head, and then regained consciousness kneeling on the ground soaked in blood. Quite an interesting experience really, and the closest anything has ever come to knocking me off my feet in quite a while.
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Unread postAuthor: bigbob12345 » Mon Jan 28, 2008 10:02 pm

Ill run some numbers through a calculator to see how effecient my gun will be and the story about the oxy/mapp hybrid explosion reminds me of when I got shocked by a camera flash I fell unconcious for a couple seconds and my entire body felt tingley for a couple hours.

Edit: ran those numbers through a calc and it will have a c:b ratio of about 0.4:1
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Unread postAuthor: DYI » Mon Jan 28, 2008 10:11 pm

Believe me, I've been shocked flash caps, and by things by things a lot worse than that (think: mains), and it doesn't compare to being taken out by that hybrid. I seem to be fairly injury resistant though. Not to the extent that Rag is, but enough to be useful in a hobby like this.

To give you an idea of the violence of this failure, lamps were knocked over in my front porch, and there were pictures and ornaments down all over the house. My parents were drinking coffee at the time, and it spilled on the table. I'm incredibly lucky that my eardrums are still intact really.

And at the pressure you're planning on using, you want to aim for something like 0.1:1 - 0.2:1, unless you can't practically make the barrel any bigger.
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Unread postAuthor: bigbob12345 » Mon Jan 28, 2008 10:19 pm

I belive you that that was much more violent that being shocked by a camera flash I havent had many falures exept when I found some 2.5in electrical pipe and Im all exited thinking tennis ball barrel and bought it got home screwed it onto my combustion and boom the entire barrel shattered but not very violently.And I guess I could use a 1.5in barrel instead to give a ratio of.Will edit with ratio

Edit:ratio of .213:1 which is better but still not perfect
Whats the ratio of your SCTBDC
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Unread postAuthor: DYI » Sun Feb 03, 2008 9:11 pm

Sorry about the late response. The C:B ratio for the current SCTBDC is ~0.16:1 with the 3" x 144" barrel (which I'm not allowed to use in my yard anymore after the incident with the door :roll: ), although that doesn't take into account the valve and the rather larger volume needed to allow breach loading (figure at least another 10 ci for that, maybe more). The new version is actually less efficient than the older version (which may have achieved the most power anyone here has ever squeezed out of half a cubic foot of air), but it makes less noise than my spray'n'pray handheld combustion, if you can believe that.

Keep in mind that the SCTBDC runs at 500 psig. Your current ratio is already approaching maximum possible performance for your current chamber size and pressure, and without changing some other variable, you're not going to squeeze much more power out of it than you already have.
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