SpudFiles

i am designing a 400psi all copper triggered burst disk cannon and want to shoot nail darts from it. i will be using some 2 1/2in sharpened nails with a expanding foam sabot so it will fit in 1inch copper (the large bore is so it shoots faster )

My question is what should i use for a tail? it would NOT seal against the barrel and would preferabley be soft so that the sabot behind it would not smash it with the massive acceleration.

btw this gun will be capable of shooting a nail at mach 1 so i think i will get some CRAZY penetration. ( steel anyone?)

c11man wrote:...400psi...

...this gun will be capable of shooting a nail at mach 1...

Fraid not. Going supersonic with 400psi air just can't happen.

As for the tail... I'm certain there's a heck of a lot of posts about this, did you consult the button of seeking? Type nail dart into the quick search and I can see several versions already.

Range from the tips of sealant cartridge nozzles to unravelled string.

I do use string for nail darts, also solid slugs of plastic, both work at the short range I'm firing it over.

and why cant it happen? it is a burst disk so it is pretty much instanty open.

ggdt says that i could get 1202fps. what i am afraid of is that i am not putting in the correct weight for the dart. How much do you think the nail weighs?

and yes i did search i found paper cones, too weak, milk jug cones, tried to make but plastic is too thin, and ones usiing fly materials are unavalible for me.

c11man wrote:ggdt says that i could get 1202fps.

GGDT is known for being rather overgenerous around the sound barrier. I suspect you'll be closer to 1000 fps, but not knowing enough about your cannon to model it in Apocalypse, I can't tell you for sure.

Still very fast, but it's almost certainly not supersonic.

As a general rule, assume if you're using air, regardless of pressure, you cannot exceed the sound barrier.
Obviously - before anyone links me to the Airforce Condor - there are some exceptions. However, these are few and far between, and somewhat (and logically*) exceptional.
*Well, what else is an exception except for something exceptional?

Also, a super fast valve doesn't change the supersonic capability of a cannon.
Quite the reverse, I have a theory that burst discs actually harm the transonic potential of a cannon.

Mind you, you're probably not looking to hear one of my lengthy dissertations on advanced air cannon mechanics, so I won't trouble you with the specifics of that theory.

depending on how big a chamber and barrel you deciding supersonic could be very possible at 400psi although your barrel would need to be at least a good 5-6 ft long.for dart ammo i use multiple peices of bailing yarn made into a tranquillizer like dart around the back of the ammo and held on with wire. also if you really want to get speed: smaller diameters + longer barrels = more velocity not the other way around their are air cannons and c02 which is even lighter than air(not just oxygen) capable of propelling a projectile over the speed of sound

Spudtyrrant, please, if you don't know something, it's not usually a good idea to make it up.

spudtyrrant wrote:supersonic could be very possible at 400psi although your barrel would need to be at least a good 5-6 ft long.

No, like I said above, not with air.

Just like having 4 people pushing a car won't get it to 100 mph any more than having one person push it, 400 psi of air will not get a projectile supersonic any more than 100 psi. That is to say, it won't go supersonic.

There are VERY exceptional circumstances under which it can happen. I doubt c11man has considered any of them.

also if you really want to get speed: smaller diameters + longer barrels = more velocity not the other way around

As far as sabots are concerned, you can achieve a greater energy in the saboted projectile with a shorter, wider barrel.

As long as the increase in barrel diameter in combination with the sabot's density decreases the overall sectional density in the barrel, this technique is perfectly workable for achieving greater velocities in a shorter barrel.

After all, why do you think the military uses discarding sabot kinetic penetrators (fired at around 1,600 m/s, about twice as fast as a typical rifle bullet), unless the use of a sabot could allow them to do exactly that?

c02 which is even lighter than air capable of prepelling a projectile over the speed of sound

CO2 is approximately 50% MORE dense than air. It's speed of sound is much lower, and it's potential maximum velocity is closer to 800 fps.

Helium or Hydrogen would help, and would almost certainly guarantee supersonic results, but they're a little hard (read: expensive) to get hold of in meaningful quantities.

i agree with some of those statements i wasn't thinking what i said about co2(i was thinking about dry ice for some reason). their are plenty of pump pellet guns and co2 pistols that can break the sound barrier using about 800psi. lewis and clark had an air gun in the 1800's that could shoot roughly 1000fps with 50 cal round their are plenty of cases where air pressure and co2 have broken sound barrier. heck even some people are getting 1000fps with marbles out of a small copper piston gun at only 300psi(i know thats not over the sound barrier i am just giving an example) all i'm saying is if he builds it right makes it long and couples this with a burst disk it is quite possible that he could reach mach 1

If you make a jig it will be easy to make them reasonably quickly and accurately, they will be stable in the barrel and your sabot doesn't have to be a complicated shape.

you could also try takinga few small pieces of yarn (1 inchish), then wrapping another piece of yarn around them and the nail, works good for breech loaders, not so well for muzzle loaders. when you finish iit should look like a squid

Hotwired wrote:Fraid not. Going supersonic with 400psi air just can't happen.

You can get pretty damn close though

You could simply attach a piece of rope/string to the nail. The rope will simply be dragged behind the projectile, holding it straight.
Did this with a drill bit once. Worked perfectly.

spudtyrrant: as you get closer to the sound barrier it gets VERY hard to go over it with compressed air.

am i understanding this right?

so i should be ecpecting around 1000fps instead of the 1202?

for the dart i think i will use just some yarn or twine attached to the back for a stabalizer. for the sabot i would use a solid foam disk at the back of it and a foam disk with a hole in the middle and cut in half so that it fitts over the nail and falls off after it is fired

the gun would have a 1 1/2 by 24inch chamber and dual 1inch unions and the area between the unions would be pioleted by a qev

The best nail darts I've found are the powder fastener nails( aka remington, paslode, RAMSET, etc) just push the orange finned collar to the back of the dart and use a sabot... an fyi, these things are perfect in a .40 cal blowgun barrel with just a wad of paper as a wadding... They're also hardened for use in concrete and steel...that's what they're designed to penetrate... midlle compartment in the row second from the right...

c11man wrote:so i should be expecting around 1000fps instead of the 1202?

More or less. You might get a little more than that, but 1000 fps is about the upper limit of what should be expected from a pneumatic.

You might get more, but don't expect it.

spudtyrrant wrote:There are plenty of pump pellet guns and co2 pistols that can break the sound barrier using about 800psi

Very well, name me the CO₂ pistols which can break Mach 1 in air.

For these purposes, I am considering Mach 1 to be 1125 fps, or 343 m/s

EDIT: Spelking Misstooks.

spudtyrrant wrote:There are plenty of pump pellet guns and co2 pistols that can break the sound barrier using about 800psi.

As Ragnarok pointed out, PCPs that go supersonic like the Airforce Condor do so with 3000 psi on tap, and with CO₂ don't even come close.