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Sabot idea

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Sabot idea

Unread postAuthor: SpudFarm » Fri Nov 12, 2010 12:50 pm

I have been a exchange student for two weeks and that gave me an idea. I saw some bolts that was treaded on the middle and smooth on the ends.

The idea was to basicly cast a epoxy slug around a HEX-nut fitting the bolt threads, then saw the slug/nut into three pieces lengthwise. The slug would fit the diameter of the barrel, perhaps with a O-ring.
When you have done this you have three pieces that can be placed "around" your penetrator over the treads and then loaded in the barrel.
It would not stick to the projectile, no way it will fail in the barrel, it's relatively light and probably reuseable if you manage to make them light.

Styrofoam should work as a "filler material" around the nut to, just have a aluminum plate at the back to protect it from the pressure (Plate seated against nut) and it could probably be made much lighter then epoxy.

Since I allways have a hard time explaining what I mean in English without making a mess of it I drew a diagram of what I mean.

I want to have some projectiles that will be great fun before I fix my hybrid again.

Image

Thoughts?
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Unread postAuthor: skyjive » Fri Nov 12, 2010 12:59 pm

Looks like a good idea. My only concern would be that the interface between the threads would not give enough grip to keep the pieces from coming apart under the high forces of a launch. Certainly if your epoxy casting didn't fit the barrel tightly and the sabot had room to expand outward it would fail. Otherwise might work well. Sounds like one of those things that has to be tested.
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Unread postAuthor: SpudFarm » Fri Nov 12, 2010 1:44 pm

The sabot will be cast inside a section of the barrel so it should fit perfectly, atleast lead slugs fits very well.

The only problem that I can se is that I might have a hard time cutting it up without removing to much material. If I use a angle grinder ETC I will remove atleast 2mm for every cut and thats way to much.
The only way I see to fix this is to cut up lots of nuts and pick out random pieces of them until I find the perfect combination. Then put them on the penetrator and have a thin layer of plastic running the length of the mold (Passing through the cuts in the nut) forming three seperate chambers for every part of the sabot.

I could probably cast 0.5m long sabots with nuts in even distribution on the penetrator and cut the length as I need it. a 1m long penetrator could be fun :)

I am sorry that I write so much, brainstorm and I hope to get feedback!

Edit: Barrel bore: 42.7mm And the diameter and length of the penetrator is not known yet.
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Unread postAuthor: jackssmirkingrevenge » Fri Nov 12, 2010 5:28 pm

skyjive wrote:My only concern would be that the interface between the threads would not give enough grip to keep the pieces from coming apart under the high forces of a launch.


Well, it's exactly the sort of interface used in military APFSDS projectiles:

Fr. Frog wrote:Operating pressures of the M829 series are between 74K psi and 96K psi depending on the particular variant.


Granted the above is precision made military hardware, but I think it would work well on this scale. I would however add a concave face to the sabot in order to promote petal separation on leaving the muzzle.

It's great to see some sort of optimisation or projectiles, large bore hybrids are already impressive beasts but with such projectiles you'll exploit the penetration potential to the fullest :)
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Unread postAuthor: Selador » Fri Nov 12, 2010 7:26 pm

I don't think you'll have any problem with the threads holding for the purpose.

Also don't think that the amount of material you take away, making the cuts, is going to make much of a difference, if any at all.

I would use bondo instead of lead, though.

Edit: Fully agree with JSR on the concave front surface.
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Unread postAuthor: saefroch » Fri Nov 12, 2010 9:14 pm

Just throwing this out there as a suggestion, on the topic of sabots:

To avoid the loss of material when you're cutting the sabot into sections, it might be possible to use wood or plastic instead of metal and split it by forcing a thin blade through it, so that a cutting implement that removes material is not required.
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Unread postAuthor: SpudFarm » Sat Nov 13, 2010 9:37 am

Well, it's exactly the sort of interface used in military APFSDS projectiles:

Yep, that's why I thought about it when I saw the bolts.

It's great to see some sort of optimisation or projectiles, large bore hybrids are already impressive beasts but with such projectiles you'll exploit the penetration potential to the fullest :)

I really love making projectiles that give results. I do think that this is the way to go on "large" bore hybrids.

The concave shape will be added, I just didn't draw it into this diagram since this was mostly about the threads.

Also don't think that the amount of material you take away, making the cuts, is going to make much of a difference, if any at all.

I think it will, mostly because there will be big gaps for the gas to escape around the sabot. I have a image in my head how I could fix that though.
I will try to draw a more complete version once I get home tonight.

To avoid the loss of material when you're cutting the sabot into sections, it might be possible to use wood or plastic instead of metal and split it by forcing a thin blade through it, so that a cutting implement that removes material is not required.

I have tried wood but it's so damn hard to get it to perfect shape without a lathe.

Also, the filler material will probably be epoxy or something. I have more thinking to do. I want those to be as light as possible so they don't get enough energy to burry themself in the ground or pulverize on impact with something.
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Unread postAuthor: jackssmirkingrevenge » Sat Nov 13, 2010 10:04 am

This might be a bit complex but should work, pre-cut the nut sections, then when it comes to casting the filler, separate the sections with layers of thin plastic held together with grease, so when you pop the casting out it will aready be in parts, with minimal gaps.

Why not however have a one piece "cup" sabot?

Or have full bore fins front and back, so the sabot can be a simple disk, like so:
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Unread postAuthor: SpudFarm » Sat Nov 13, 2010 7:40 pm

This might be a bit complex but should work, pre-cut the nut sections, then when it comes to casting the filler, separate the sections with layers of thin plastic held together with grease, so when you pop the casting out it will aready be in parts, with minimal gaps.


That was what I was reffering to earlier in this thread: "Then put them on the penetrator and have a thin layer of plastic running the length of the mold (Passing through the cuts in the nut) forming three seperate chambers for every part of the sabot. "
I think it is a great backup method but I have my mind set to something else right now.

The fullbore fins is a good idea, might turn out to be a better choise. However, I am looking to penetrate as much steel as I possibly can, eight (Or six) fins welded in place will be hard to rip off when it pass through the hole.
One of the goals I have with the cannon is to set up a targer that resembles a lightly armoured personell carrier or something and try to penetrate it and cause secondary damage on the inside to a melon in a kevlar west or something.

I don't have time to draw up what I mean tonight, I will give this some thought before going to sleep and I probably come up with something else aswell.
I want something that can be made fairly easily and cheaply so I can fire three or so of them every day at different targets. Penetrators are huge fun and great high speed material :)
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Unread postAuthor: jackssmirkingrevenge » Sun Nov 14, 2010 3:39 am

SpudFarm wrote:That was what I was reffering to earlier in this thread: "Then put them on the penetrator and have a thin layer of plastic running the length of the mold (Passing through the cuts in the nut) forming three seperate chambers for every part of the sabot."


You're right, I hadn't read it properly :roll:

The fullbore fins is a good idea, might turn out to be a better choise. However, I am looking to penetrate as much steel as I possibly can, eight (Or six) fins welded in place will be hard to rip off when it pass through the hole.


Why not a two part sabot? O-ring friction will keep the fins in place during flight, then they slide off on impact. That's the theory at least, I'm guessing it would be pretty friggin' mangled too and not exactly be reusable.
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Unread postAuthor: SpudFarm » Sun Nov 14, 2010 7:54 am

Genious :shock:

That would probably be my ultimate solution to, you came up with it in a matter of hours! :)

I will try the threads also though, some variation can't harm..
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Unread postAuthor: jackssmirkingrevenge » Sun Nov 14, 2010 10:50 am

SpudFarm wrote:That would probably be my ultimate solution to, you came up with it in a matter of hours! :)


To be honest for most of those hours I was out imbibing copious quantities of fermented wheat :)

Silly question, why not just eliminate the fins completely and use a hollow tail for stabilisiation?
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Unread postAuthor: SpudFarm » Sun Nov 14, 2010 11:22 am

Haha!

The reason I can't do that is because I would need a lathe or a mill. I have access to those at school but I don't think they like what I am using them for :P

And those will not have any chance to hit perfectly if they exit the muzzle at a slight angle, they will probably start to wobble. I just have a crush on fins :)

Edit: How hard are those bolts marked 8.8? I know they are heat treated but how will they compare to normal steel plates?
Also, since they are heat treated they can probably be hardened further?
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Unread postAuthor: jackssmirkingrevenge » Sun Nov 14, 2010 11:48 am

You could probably make one on a decent drill press but fair enough, I can understand a fin fetish - APFSDS projectiles are undeniably sexy :)
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