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Burst Disk Projectile

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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Burst Disk Projectile

Unread postAuthor: kenbo0422 » Tue Sep 29, 2009 12:50 pm

For a lack of a better term, here is what I call a burst disk projectile. It replaces the burst disk on any system where the projectile can be either breech loaded or in semi automatics where the projectile is loaded from a magazine. It can be used for hybrids or combustions. I have maybe mistakenly placed it here on the hybrid discussion only because I consider it a part of the cannon make up rather than just another projectile.

The lips in the aft part will hold the projectile in place at the very beginning of the barrel and the disk will hold the lips out. Open cell foam is used to allow the pressure inside the chamber to equalize on both sides of the retaining disk. When ignition occurs, the foam will collapse as the disk pushes on it, clearing the retaining lips. Pressure behind the projectile will dislodge the lips from their retaining 'ring' as is moves forward and out the barrel.

This will give you a clean shot from chamber to barrel. It can also be incorporated into a preloaded cartridge design.

The shell only needs a couple of O-rings where it sits waiting to be fired in order to seal off the chamber from the barrel.[/img]
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Burst Disk Projectile.PNG
This is my projectile design to eliminate a burst disk and pistons. Can be used for cartridge designs as well.
Burst Disk Projectile.PNG (13.4 KiB) Viewed 1234 times
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Unread postAuthor: jackssmirkingrevenge » Tue Sep 29, 2009 1:58 pm

Interesting concept, but does it offer any real advantage in reduced complexity compared to simply replacing a burst disk, or having a tight fitting projectile in a seal, given the complexity of making the projectile which is unlikely to survive in a state that will allow it to be reused.
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Unread postAuthor: kenbo0422 » Tue Sep 29, 2009 4:46 pm

Most of my projects have never fired a spud, let alone any other vegetable. The burst disk, to me, was always the lamest excuse for getting a good clean pressure release. It has at least the same complexity as this with the added fact that it insures that you won't re-use it. This has the ability to be recovered, even though I've never recovered a bullet except for a damage inspection. Even with total destruction, this projectile is actually easy to make with PVC, some glue and a hacksaw, and can be made quickly and in large numbers. The burst disk is at least as complex in that you have to sandwich a layer(s) of plastic, paper, or aluminum between two O-rings, must be cut correctly and you literally have to take the launcher apart to reload it.

The design also goes beyond just the burst disk replacement. It can be incorporated into a cartridge that can be precharged at greater than atmospheric pressure. A semi-auto setup can be used with it because it allows for a magazine to load it, even without a cartridge, automatically setting up a condition for hybrid charging and launching.

This design also offers something else. The projectile doesn't have to be a 'bullet'. It can be used in a sabot configuation, which is 95% recoverable. This is what I have the most use for. It gives me a higher area with a smaller steel pin for punching power, even with diameters of only 1". I've recorded close to mach 1 in an inline rifle configuration.

This also gave me the inspiration to make a bolt action rifle for hybrid operation, knowing I wouldn't have to replace a burst disk or put a piston in the way of a straight through bolt loading design.
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Unread postAuthor: spudtyrrant » Tue Sep 29, 2009 5:28 pm

kenbo0422 wrote: Even with total destruction, this projectile is actually easy to make with PVC, some glue and a hacksaw, and can be made quickly and in large numbers. The burst disk is at least as complex in that you have to sandwich a layer(s) of plastic, paper, or aluminum between two O-rings, must be cut correctly and you literally have to take the launcher apart to reload it.
This may work well for cartridge but using a burst disk is extremely cheap compared to the idea proposed, plus less time consuming. Using this design you would be subject to using one specific type of projectile instead of the many different kinds that can be used with a traditional set-up, it seems with only real gain with using this set-up would be loading time, but i don't think its really worth it :?
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Unread postAuthor: psycix » Wed Sep 30, 2009 4:13 am

I recommend to put o-rings in grooves on the inside of the barrel. A tricky thing to do without a lathe, but it would save you from having to use a set of o-rings on each projectile.
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Unread postAuthor: inonickname » Wed Sep 30, 2009 4:37 am

psycix wrote:I recommend to put o-rings in grooves on the inside of the barrel. A tricky thing to do without a lathe, but it would save you from having to use a set of o-rings on each projectile.


Not really. For example if using copper pipe you could just use a coupler which would allow you to add a seal the size of the pipe. Anyway, for a projectile like this o-rings are hardly adding much complication.

Simply seems like an over complication that limits the projectiles you can use.
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Unread postAuthor: kenbo0422 » Wed Sep 30, 2009 4:59 am

The O-rings I use are square type, and yes, they are in the barrel, not on the projectile.

One of the main ideas with this, as mentioned by spudtyrrant, is to save time with loading. Especially in a 'sniper' style situation.

What I don't get, is that there are many projects on this site that have homemade ammo, even as simple as casting your own bullets. Why is this considered a PITA? I cast my own bullets and reload for several rifles and pistols, but you don't find me complaining about that. I find this easier than loading shells for a real rifle. BTW, the steel pin sabots rounds I talked about earlier are for hunting. Around here, coyotes have become a problem and this just so happens to be able to take down a coyote as well as my 22 magnum does. (Well, it doesn't have the range :( )
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Unread postAuthor: Technician1002 » Wed Sep 30, 2009 5:08 am

This is easier then it first appears. I did this on my Dragon Cannon and one of my much earlier designs. When you glue the barrel into the coupling, make this simple modification.

1 cut a ring of PVC off the end of the barrel about 1/4 inch long. Use a miter box and get the cut straight. Take the piece and sand it smooth on the cut. Do the same for the end of the barrel. Sand it smooth and ensure the cut is square.

Glue the ring all the way in a coupling. Slide in an o ring next to it. Glue in the barrel next. Done. If desired the coupling can be cut off right at the end of the ring in the coupling.

If you grease the ring before adding the barrel, it won't glue the ring in place. Keep the grease off the surface that will be glued.

Edit Added photo of an o ring in a piston cylinder using a cut piece of pipe to make the groove.
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O ring for the 3 inch piston inside The Dragon cannon.
Last edited by Technician1002 on Wed Sep 30, 2009 7:39 pm, edited 1 time in total.
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Unread postAuthor: inonickname » Wed Sep 30, 2009 5:17 am

Please keep hunting off of here, ESPECIALLY with a gun you have made.
The rules.

To get it even working at first would be a lot of work, and to manufacture each round to specifications that are acceptable will be time consuming and difficult, much harder than pouring molten metal into a mold. Plus, any mistake in manufacturing will result in premature firing. A poorly made burst disk is hard to come across, and will basically not pressurize.
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Unread postAuthor: kenbo0422 » Wed Sep 30, 2009 5:32 am

A lot of work... hmmm....

:roll:

Premature firing?? How?

Sorry about the hunting reference. Like any other place, the rules are read and far from thought when trying to make a point.
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Unread postAuthor: jackssmirkingrevenge » Wed Sep 30, 2009 5:34 am

inonickname wrote:A poorly made burst disk is hard to come across.


Unless of course you aim carefully ;)

kenbo0422 wrote:A lot of work... hmmm....

:roll:


Do you have any manufactured prototypes you'd care to share?

I would propose this to be a simpler solution, a slightly narrower breech where the projectile is wedged hard enough not to be moved by the mixture gasses but is then dislodged on firing. In order to remove some of the guesswork a detent could be added and adjusted until the optimal retaining force is achieved.
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Unread postAuthor: kenbo0422 » Wed Sep 30, 2009 11:07 am

Actually, I like your idea with the detent, better. Its so simple, its brilliant! :oops: The O-rings would give you minimal friction, enough to allow a seal at say, a 4x mix with 3 O-rings. My rifle has an aluminum block right about there which would accommodate a spring loaded detent perfectly.

I still think my original idea would do some good for a cartridge. The easiest material/preformed slug is a plastic cryogenic sample tube ( PP )that you can get on Ebay, etc. for next to nothing for hundreds of them. I was lucky in that the company I work for was throwing them out after deciding they weren't what R&D was looking for. I have a few thousand of them...
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Unread postAuthor: Hotwired » Wed Sep 30, 2009 5:50 pm

You may be interested in this one if you like preloaded cartridges, except it's not a cartridge, the entire object launches: Hybrid RPG

It's quite a lot safer than my pneumatic take as it has a lower pre-firing chamber pressure and the burst disk is totally enclosed in the rear. Even simpler to make as well.

I'll make it someday :)
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Unread postAuthor: jackssmirkingrevenge » Thu Oct 01, 2009 1:33 am

kenbo0422 wrote:Actually, I like your idea with the detent, better. Its so simple, its brilliant! :oops: The O-rings would give you minimal friction, enough to allow a seal at say, a 4x mix with 3 O-rings. My rifle has an aluminum block right about there which would accommodate a spring loaded detent perfectly.


I used the detent system on my latest, have a look.

I still think my original idea would do some good for a cartridge. The easiest material/preformed slug is a plastic cryogenic sample tube ( PP )that you can get on Ebay, etc. for next to nothing for hundreds of them. I was lucky in that the company I work for was throwing them out after deciding they weren't what R&D was looking for. I have a few thousand of them.


That would explain your enthusiasm, if you already have the stuff available ;) I agree, making your own ammunition isn't maybe as tedious as has been expressed above, however I think the majority prefer to put the effort into their launcher then shoot it with relative leisure.
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