Sneak peak of my new build. Pic of 4'' piston and 2.5"

[jhalek90]

Just wanted to tease you all a little bit with some pics of my new cannon/ammo

Pic of the piston. Fits perfect in sch 40 4'' pvc.



Pics of the new round. Easy to make. snug fit in barrel.


Tail of the new round.



the cannon itself is still in the works. It its a Co-axial
With 4'' x 4' chamber and a 3" barrel.

right now it is goin to be piloted with a modded 1'' sprinkler. but i may have to change that if it is to slow.

SIDE NOTE:
I have also successfully made a frag round, and may post details in a few days... after some testing.

it basically works like this, head of round hit target, compresses an inner piston, which blows a burst disk in the back of the round, sending steel or plastic bb's every where.

Hope you like... questions? comments?

[elitesniper]

NO comment i know its goign to be crazy!:]
i love coax's

[rp181]

Awesome. Rather then having the burst disc on the back, it would be interesting if it was put on the side.

[jackssmirkingrevenge]

Looking good, it would be nice to see a diagram of your "frag" round

Also, might I suggest you "add lightness" to your piston by grinding down the bolt and using a smaller ordinary nut. Not only will you save some weight which means better opening times and less stress on the launcher, but you'll also reduce turbulence for air entering the barrel, which equals better performance.

[jhalek90]

Looking good, it would be nice to see a diagram of your "frag" round

Also, might I suggest you "add lightness" to your piston by grinding down the bolt and using a smaller ordinary nut. Not only will you save some weight which means better opening times and less stress on the launcher, but you'll also reduce turbulence for air entering the barrel, which equals better performance.

Yes sir.

I had not even thought of that,
I shall do it tomorrow!

also... i think you meant "Reduce weight" as adding lightness seems kinda impossible... well... apart from helium filled rounds...

Ill try and make a diagram in paint.... post when done.

EDIT:


Probably going to need an o-ring or 2
But you should get the concept.

The cap compresses the air in the round on impact, and breaks the burst disk.

The only downside is that you will need a "Nose first" hit.
But..... that shouldn't be a problem.... he he he

[rp181]

with all that stuff in the back, its going to be unstable. You need weight in the tip to get a head on impact.

[jackssmirkingrevenge]

I think you meant "reduce weight" as adding lightness seems kinda impossible...

It's a term I picked up from my aeromodelling days

With all that stuff in the back, its going to be unstable. You need weight in the tip to get a head on impact.

Unless you're using a rifled barrel, this is certainly the case. Also, with a piston valve you're going to have a fairly violent acceleration in the barrel, my guess is that it will actually burst before leaving the muzzle as the rear of the projectile tries to accelerate while the front wants to stay still.

It's a good idea, but I think it needs a little tweaking

[jhalek90]

Hmm.... good point about it bursting in the barrel

But, what about this... a solid pvc rod it cut to make a loose fitting "PLUG" in the back of the round. It fits into the coupler and rest on the stop. on impact it would get blown out. this solves the breaking in barrel aspect of it.

[jackssmirkingrevenge]

That would however mean that unless it hits an extremely hard surface very fast, it won't burst at all. Maybe a pre-pressurised round with a schrader valve actuator at the nose would work, or a soda bottle filled with a hybrid mix and cheap piezo nosecone

[rp181]

but the valve would force the plug in. I think Your best bet is (if it doesn't work) wadding it.

[jhalek90]

hmmm i am goin to have to wait till my cannon is done to test the rounds.

Or, i might do some low velocity (throwing) test soon... hahaha we shall see how THAT goes.

[velocity3x]

Pic of the piston. Fits perfect in sch 40 4'' pvc.

I think the large diameter PVC (in any schedule) will severely limit the max working pressure. As your projectiles will be large and heavy, much pressure will be necessary to launch the projectiles with any appreciable range or velocity.

Considering the size of these projectiles loaded with BB's, I can only guess that they must weigh close to 1/2 +/- pound! What kind of psi do you intend to launch them with and how far? Considering the projectile size, weight and the enormous operating pressure required to accelerate such a large payload, I doubt that large diameter PVC can withstand the pressure necessary to launch it any appreciable distance or do it safely. I think your rounds carrying the payload in the rear may tumble like throwing a brick (if launching any serious distance) without nose weight and fins or something for stabilization.

[jhalek90]

The lowest rated part on my cannon in progress is 220 psi

so i will have no problem taking it to the 145 my compressor will allow.

[jackssmirkingrevenge]

Considering the projectile size, weight and the enormous operating pressure required to accelerate such a large payload, I doubt that large diameter PVC can withstand the pressure necessary to launch it any appreciable distance or do it safely.

Don't forget that area increases exponentially with diameter, so as calibres go up the available force increases dramatically.

100 psi in a 1 inch barrel gives you around 79 lbs pushing on your projectile.

For a 3 inch barrel, you get the same amount of force with just 10 psi.

Given this launcher will also have a fast acting high flow valve, I think performance will be impressive even with very low pressures, let alone the compressor pressures it appears it will be used at.

[jhalek90]

Yes, GGDT predicts around 300 ft/lbs of force at the muzzle.

Seems to me that that is a very high energy for such a low pressure.

Now here is a question that i have about gddt... is that ft/lbs propelling the projectile forewords? If so, does that mean the cannon will kick back at the same force per Newtonian physics?

EDIT: spelling