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best ammo

Post about things you have launched or thought about launching. Also post about various materials used for building cannons. No posts about explosive projectiles!
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Unread postAuthor: rcman50166 » Fri May 02, 2008 12:07 pm

Well I kinda went off on a tangent. I do that a lot. I didn't need to write all of that but I was curious and did the calculations and since I'm already here, I wrote it down. Also If a dart and a slug come out of the same cannon they would have the same energy ideally.
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Unread postAuthor: hyldgaard » Fri May 02, 2008 12:10 pm

rcman50166 wrote:Well I kinda went off on a tangent. I do that a lot. I didn't need to write all of that but I was curious and did the calculations and since I'm already here, I wrote it down. Also If a dart and a slug come out of the same cannon they would have the same energy ideally.

Well yea, if the dart weighs the same as the slug.. but often the led slug will be the heavier.
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Unread postAuthor: rcman50166 » Fri May 02, 2008 12:15 pm

No, based on the laws of conservation of energy they will be equal. Ek=1/2MV^2. Ek is the same if they are shot out of the same cannon. The lighter round will be faster and the heavier will be slower, but they will have the same energy.
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Unread postAuthor: hyldgaard » Fri May 02, 2008 12:18 pm

rcman50166 wrote:No, based on the laws of conservation of energy they will be equal. Ek=1/2MV^2. Ek is the same if they are shot out of the same cannon. The lighter round will be faster and the heavier will be slower, but they will have the same energy.

True, and the heavier round will keep its energy much longer than the light one.
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Unread postAuthor: Gippeto » Sat May 03, 2008 11:48 am

My slug mold for the copper gun, and some of the ammo produced with it.

I used a plastic injection molder and some hdpe beads to make the all plastic ones, and the others which have a 3/8" ball bearing in the front.

The last one is cast from lead, and has had the back drilled out on the lathe.

I will be shooting these today. :)
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Unread postAuthor: SpudFarm » Sat May 03, 2008 12:27 pm

nice work gipp!

i also casted some lead today.. i had a marble in the nose of it and on others i filled the mold with tiny nuts and screws to "arm" it.

i also casted a 500g 1" slug to shoot in the water :D
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Unread postAuthor: daxspudder » Tue May 06, 2008 5:52 pm

i nominate my hollowed fishball ammo Image
great for many uses, paint, sand, water, gelatin, flour, stuff out of glowsticks(or the stuff from united nuclear) easily sealed with electical tape, sizes for all standard barrels 2" and under, an extra foot of tape for a streamer gives a perfectly straight flight at longer distances, never ending possibilities and fun, as well as some unmentionables you can pm me for...
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Unread postAuthor: DYI » Tue May 06, 2008 9:02 pm

No, based on the laws of conservation of energy they will be equal. Ek=1/2MV^2. Ek is the same if they are shot out of the same cannon. The lighter round will be faster and the heavier will be slower, but they will have the same energy.


Ah, wouldn't it be wonderful if the world was that simple...

Unfortunately, it isn't, and in this world, there are these nasty things called efficiency losses. In gas guns at least, the higher the velocity from a given cannon, the lower the efficiency. Energy is conserved, but more is exerted on the projectile in the case of a heavier slug, as it remains in the barrel longer, not to mention the extreme losses encountered when the projectile speed approaches or exceeds the speed of sound in the propellant gas. Thus, with our gas guns, the efficiency will always increase as the mass of the projectile increases. Don't make the mistake of assuming that all available energy is exerted on the projectile.

The best simple projectiles are those which have a highest sectional density, and the lowest drag. Not suprisingly, these factors need to be balanced with the aforementioned efficiency losses with lighter projectiles and lower velocities of heavier projectiles to achieve the best performance with a given launcher.

With those factors in mind, I designed this:

Image

Unfortunately, I no longer have any operational 75mm launchers, but a simple conversion to 100mm bore could have it leaving the barrel of a current project at just over 1200fps, with a healthy 45k ft/lbs of muzzle energy.
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Unread postAuthor: daxspudder » Wed May 07, 2008 1:41 pm

thats wicked. simply wicked, i give mine a close second to that...
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Unread postAuthor: drex » Wed May 07, 2008 3:49 pm

it reminds me of the sabot(ed?) darts that they fire out of tankguns.
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Unread postAuthor: STHORNE » Wed May 07, 2008 4:01 pm

Thats a sick round DYI. very nice work.

lol, you pretty much empty a whole roll of duct tape per dart if you plan on making more for a bigger barrel.
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Unread postAuthor: SpudFarm » Wed May 07, 2008 4:08 pm

the sad part is that it is a drag bomb :P
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Unread postAuthor: STHORNE » Wed May 07, 2008 4:10 pm

DYI, I was looking over your dart when i noticed the aluminum fins.

It looks strangely familiar...did you salvage it off of something else or forge them yourself?
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Unread postAuthor: SpudFarm » Wed May 07, 2008 4:12 pm

have you seen the round he used on the 1/4" steel?
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Unread postAuthor: rcman50166 » Thu May 08, 2008 12:46 pm

Well I know about real world losses. But I esimate by ideal physics. If I had covered efficiency losses my post would have been significantly longer. Also losses are almost always estimates for me.

Like the dart round but there is a lot of energy wasted in the non removable sabot. I'm sure you already know DYI but for the sake of a free information based society, the ideal sabot is removable, provides a very tight seal, is light, and cheap. Removing the sabot provides less air resistance and more penetrating power for the round. If a sabot doesn't have a tight seal, it defeats the purpose of the design. The lighter the sabot is, the less energy from the cannon it uses. Every joule saved by the sabot's weight is a joule of energy added to the round itself. A cheap sabot is a practical sabot, unless it's reusable.
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