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

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Sneak peak of my new build. Pic of 4'' piston and 2.5"

Unread postAuthor: jhalek90 » Wed Dec 30, 2009 4:18 pm

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.
Image


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

Tail of the new round.
Image


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?
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Last edited by jhalek90 on Wed Dec 30, 2009 10:23 pm, edited 1 time in total.
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Unread postAuthor: elitesniper » Wed Dec 30, 2009 5:16 pm

NO comment i know its goign to be crazy!:]
i love coax's :D
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Unread postAuthor: rp181 » Wed Dec 30, 2009 5:20 pm

Awesome. Rather then having the burst disc on the back, it would be interesting if it was put on the side.
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Unread postAuthor: jackssmirkingrevenge » Wed Dec 30, 2009 9:35 pm

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.
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Unread postAuthor: jhalek90 » Wed Dec 30, 2009 10:07 pm

jackssmirkingrevenge wrote: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...:idea:

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

EDIT:
Image

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
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Unread postAuthor: rp181 » Wed Dec 30, 2009 11:51 pm

with all that stuff in the back, its going to be unstable. You need weight in the tip to get a head on impact.
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Unread postAuthor: jackssmirkingrevenge » Thu Dec 31, 2009 2:44 am

jhalek90 wrote: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 ;)
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Unread postAuthor: jhalek90 » Thu Dec 31, 2009 9:05 am

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.
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Unread postAuthor: jackssmirkingrevenge » Thu Dec 31, 2009 11:43 am

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 ;)
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Unread postAuthor: rp181 » Thu Dec 31, 2009 12:12 pm

but the valve would force the plug in. I think Your best bet is (if it doesn't work) wadding it.
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Unread postAuthor: jhalek90 » Thu Dec 31, 2009 1:07 pm

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. :?
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Re: Sneak peak of my new build. Pic of 4'' piston and 2.5&qu

Unread postAuthor: velocity3x » Fri Jan 01, 2010 4:55 pm

jhalek90 wrote: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.
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Unread postAuthor: jhalek90 » Sat Jan 02, 2010 9:43 am

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.
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Re: Sneak peak of my new build. Pic of 4'' piston and 2.5&am

Unread postAuthor: jackssmirkingrevenge » Sat Jan 02, 2010 10:06 am

velocity3x wrote: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.
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Last edited by jackssmirkingrevenge on Tue Jan 05, 2010 1:07 am, edited 1 time in total.
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Unread postAuthor: jhalek90 » Sat Jan 02, 2010 10:57 pm

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
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