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el cañón de la combustión de 55mm

Built a combustion 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: starman » Mon Nov 24, 2008 3:49 am

What the heck did you use for ammo there? Looked like a plastic cup....
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Unread postAuthor: jackssmirkingrevenge » Mon Nov 24, 2008 4:02 am

starman wrote:Looked like a plastic cup....


Your statement will be completely correct with the simple addition of the phrase "... full of nuts and bolts" :D

I was dissapointed to note that there was no apparent reduction in sound, in spite of the considerable reduction in chamber volume. A conventional suppressor would be far too bulky in this case, so I'm considering other optionsthat would have the added benefit of keeping the sabot within the barrel.
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Unread postAuthor: CasinoVanart » Mon Nov 24, 2008 5:07 pm

Noice idea there JSR, if only they made flame proof elephant sized condoms you would be set (and so would i) :D

remember showing me those 12 guage shells used in Vietname?
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Unread postAuthor: ALIHISGREAT » Tue Nov 25, 2008 2:46 am

jackssmirkingrevenge wrote:
starman wrote:Looked like a plastic cup....


Your statement will be completely correct with the simple addition of the phrase "... full of nuts and bolts" :D

I was dissapointed to note that there was no apparent reduction in sound, in spite of the considerable reduction in chamber volume. A conventional suppressor would be far too bulky in this case, so I'm considering other optionsthat would have the added benefit of keeping the sabot within the barrel.


what about a choke? would that quieten the beast by slowing everything down and giving it more time to cool? or is that just wishful thinking?
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Unread postAuthor: jackssmirkingrevenge » Tue Nov 25, 2008 4:09 am

The basic idea, as illustrated in the fuzzy attachment, is simply a cast epoxy plug at the muzzle end that will hold on to the sabot but will allow the projectile/s through. I sealed the cast with candlewax instead of the usual araldite so it should come out pretty easily.

The plug is held by a single bolt to allow for reloading, time will tell if this is sufficient however I'm banking on several factors such as a very lightweight (essentially paper, tissue and duct tape) sabot and the rapid cooling of combustion gasses that will instantly reduce the pressure pushing the sabot against the plug.

If it fails, and likely the point of failure would be a crack where the bolt goes through the barrel, it will simply be a question of chopping off the offending bit of muzzle and figuring out a stronger, multi-point or reinforced attachment. Testing scheduled for 24 hours ;)
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Unread postAuthor: CasinoVanart » Tue Nov 25, 2008 3:07 pm

I bet that the sabot will reseat itself once fired JSR, that or get sucked into the chamber 8)
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Unread postAuthor: jackssmirkingrevenge » Tue Nov 25, 2008 4:16 pm

I just hope it won't come sailing out the front end taking half the barrel with it :roll: In my mind a lightweight sabot shouldn't have much clout, and if I can avoid the projectiles hitting the plug I should be fine - but as always in the world of spudguns, you never know.

We'll find out tomorrow :)

edit: took some photos of the finished plug, installed and removed. It's looking a bit wobbly, I have a bad feeling about this...
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Unread postAuthor: CasinoVanart » Tue Nov 25, 2008 9:29 pm

Bwahahaha, things go wrong when you have a good feeling Jack!!! Be sure to video the hurrendous failure for us all to enjoy :D

Jks, good luck brother :)
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Unread postAuthor: ALIHISGREAT » Wed Nov 26, 2008 2:47 am

it all depends on the weight of the sabot, if you put your gun through HGDT you could find out what kind of energy the sabot will have?
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Unread postAuthor: jackssmirkingrevenge » Wed Nov 26, 2008 3:03 am

ALIHISGREAT wrote:it all depends on the weight of the sabot, if you put your gun through HGDT you could find out what kind of energy the sabot will have?


Too late, I already put the sabot through the gun :roll: and here's the result:

[youtube]http://www.youtube.com/watch?v=vNF4yPAP4hc[/youtube]

The sabot was a paper-and-duct-tape cup with a foam insert cut from a pool noodle. It doesn't show on the video but the foam actually managed to squeeze its way through the hole in the plug, unlike the paper cup which stayed in the barrel. This would explain the fact that the shot was still pretty loud, though still quieter than usual - note the lack of complaining colleagues in the background :)

Unfortunately, if you look at the plug, there's a large crack where the bolt sits. I don't think it will take another firing, time to contemplate and make some changes.
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Unread postAuthor: starman » Wed Nov 26, 2008 11:10 am

Errr um Jack, I frankly have no idea what you were trying to accomplish or how you accomplished it with the whole muzzle-tip-choke and duct tape/cup/noodle sabot thingy.

- I can't figure how the noodle sabot is expected to exit the epoxy choke hole?.? I am missing a critical detail obviously.

- The epoxy choke hole is mounted at the exit end of the barrel...isn't it? or not?
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Unread postAuthor: jackssmirkingrevenge » Wed Nov 26, 2008 12:08 pm

Yes, the plug is at the muzzle, and the point is that the sabot shouldn't exit the barrel, only the projectile contained within it.

Basically, most of the noise from a combustion cannon comes from the rapidly expanding hot gasses exiting the muzzle after the projectile. A conventional silencer gives the gasses space to expand before exiting, thereby reducing their pressure and therefore noise.

With this system however, the idea is that the gasses don't leave the barrel at all, blocked by the sabot at the muzzle. It's not a new idea, the Russians have several weapons chambered for special "captive piston" cartridges that use the same concept:

Image

unfired cartridge

Image

firing

Image

piston jammed against cartridge, projectile fired.

The US developed a similar cartridge for use by Tunnel Rats in Vietnam and used in the Quiet Special Purpose Revolver which fired 15 tungsten balls each with the muzzle energy of an adult 0.177 air rifle.

They also created the AAI "telecartridge" that could be fired from unmodified 12 bores and used a metal "balloon" to contain the gasses instead of the piston, here's the unfired cartridge on the left and fired one on the right:

Image Image

This is basically the effect I was trying to replicate the for my combustion. A conventional suppressor design with baffles and an expansion chamber would work, but would be too bulky in my case. The above design were created for the same reason, being silent *and* compact.
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Unread postAuthor: Radiation » Wed Nov 26, 2008 12:46 pm

The problem is that the gun you referenced is an airgun. It is more silent naturally. With a combustion based gun the only way to silence the sound is by (as you said) giving those gasses somewhere to expand before exiting the barrel OR by sopping up the heat and therefore energy of the exiting gasses either by an advanced baffling system or condensing the expanding heat on a thermally conductive surface such as steel wool etc. Your design seems to do neither and is relying on a silencing method designed for an airgun which operates on an entirely different set of principles (I know I don't have to tell you all of this, it's just me thinking out loud to try to figure out your design a little better.)

I guess I just don't understand the physics of how this actually would silence a combustion reaction?
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Unread postAuthor: starman » Wed Nov 26, 2008 1:18 pm

jackssmirkingrevenge wrote:Yes, the plug is at the muzzle, and the point is that the sabot shouldn't exit the barrel, only the projectile contained within it.


Oh. Then I'm thinking you're going to want some heap-big strong muzzle choke, maybe a thick rubber piece captured behind a very substantial ring plug on the end of a metal barrel. The heat and mechanical stresses on that thing are going to be large.

How are you guaranteeing the projectile hits the center of that doughnut? and doesn't jam in there and make for a bad day? I would say you could taper it but you'll want a fairly blunt edge in there to catch and stop the sabot.
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Unread postAuthor: ALIHISGREAT » Wed Nov 26, 2008 1:22 pm

How are you guaranteeing the projectile hits the center of that doughnut? and doesn't jam in there and make for a bad day? I would say you could taper it but you'll want a fairly blunt edge in there to stop the sabot.


i would simply make the doughnut's id slightly larger than the projectile id...
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