Killjoy's FEAR

[Killjoy]

Thanks for the comments you guy

I am trying to find time to redo the tests, but i have tests and a lot of school work and stuff i need to do for my employer, but hopefully i can do some tests this weekend.
The golfballs were not going 2700 fps, they were actually goin 1500 fps, mainly because i didn't feel like properly wadding them in the barrel.

The barrel slides foreward because the way i attached it to the burst disk holder was not very effective, and the pvc barrel was constantly ripping out of the holder due to the force of the expanding gases. Its been fixed though so the barrel should stop moving forward.

Oh and sorry about the junk, as soon as i finished the project my parents made me clean up the rest of the house and back yard, and everything ended up in my garage, but i should have some clearer pics by the end of this weekend if i do get a chance to fire this cannon again.

[paaiyan]

That is a beast. You should try packing in some lead sinkers with good wadding, I'd wanna see the damage from that.

[Killjoy]

Well actually i have a whole bunch of 1" steel ball bearings i was planning to use...

[paaiyan]

Oh hey, that works too. You know what else would be awesome, get one of those packages of .177 BB's and load a buttload of them in it, like a puntgun, haha.

[AmYisroelChai]

Just signng in to say very nice cannon.
Good work. Keep us informed of all the stats.

[SpudBlaster15]

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[Hotwired]

The longest range black power rifles won't exceed 2,000 feet per second, I find it hard to believe that a mix of propane and air can do better.

Are the barrels of said black powder rifles FIFTY FEET long? I don't think so. The 2700fps figure sounds accurate for a 4x hybrid launcher of this scale.

Put a fifty foot barrel on a rifle and the drag will kill the bullets speed, not make it go faster.

The best modern sniper rifles don't do more than 900m/s (~2900fps) and thats with the massive acceleration from around 50,000psi of hot combustion gases.

The .50 rifle shown earlier does 2700fps
The chrony reading for the potato also showed 2700fps

I'm an engineering type so it's in my nature to doubt the ability of a possibly disintegrating potato of large diameter to be travelling at the same speed as a much thinner, aerodynamic bullet fired from the most powerful sniper rifles around.

The speed in question being almost three times the speed of sound.

Ask yourself what kind of materials and shapes you know of that can go that fast - missiles, bullets, some jets - then consider a 2" potato slug which has just passed through fifty feet of pipe.

Thats why I suggested the chronographing of a blank fire and a solid round of equal mass. I'll accept the readings from that when they happen.


ShowNoMercy of course I'm jealous, I'd be looking at the inside of a police car within half an hour if I tried to fire something as big and powerful as this round my place

[YElloW]

Kill joy, your barrel is a bit long, you might get better results from a 25-30 foot barrel, also, in reality, your best shot from the cannon would probably have a speed of 2000 fps to 2300 fps with a golf ball, which would have the KE of 15,000J-21,000J. You might be able to get better penetration and speed from a finned steel sabot which I can tell you how to make, if you want to know. Besides your choice of ammunition, you have a superb cannon, which none will match.

You have my vote as the best cannon. I love how you have everything electronically controlled, just get me some more pictures.

[Killjoy]

Thanks spudblaster.

Hotwired,
I understand your reasons for questioning the results, and am currently trying to make time to test and make sure i have not made any mistakes and that the recorded velocity is accurate, or maybe not.

Yellow,
The barrel in my opinion is not overly long, i still have about a 1 to 1 ratio which should work fine, and it does so i am content with the barrel length, but thanks for your suggestion.
The finned sabot is agood idea though, might try that some time.
Thanks for your vote by the way.

[SpudBlaster15]

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[Hotwired]

I'm not going to requote all of that or deviate from what I'm trying to say so:

For a 100g slug of potato, 50 feet of 2" pipe and a house sized volume of 220psi air GGDT says about 9000J and 1400fps. For a 50g slug with the same launcher: 8586J and 1923fps.

I think the 2700fps reading was from particles of potato which were taken off the slug through the friction of the barrel.

Nothing more I can say right now but I hope the cannon does well in the competition

[jackssmirkingrevenge]

All this debate is in the air and superflous until killjoy manages to chrono a series of solid projectiles far enough from the muzzle for the blast effect to be negated.

Data is irrelevant unless its repeatable.

[DYI]

Sorry for kicking this up, but I was looking at the thread and saw Hotwired's GGDT numbers, so I input the parameters of this cannon and got exactly 2700 fps and 12488 ft/lbs for a 50 gram projectile, with 300psi CO2 at 3500 degrees farhenheit. These numbers are obviously not perfectly accurate, since the combustion produces CO2 and H2O, and doesn't occur instantly, and GGDT isn't the most accurate with supersonic projectile velocities, but it would certainly seem as though the 2700 fps number is within the realm of possibility. see SCTBDC-100 thread