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51mm Anti-Tank

Built a pneumatic cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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51mm Anti-Tank

Unread postAuthor: thedeathofall » Wed Jul 29, 2009 9:33 pm

Well, i have finally gotten around to finishing this thing. (Why do I even bother calling it finished? I will forever be upgrading and downgrading and messing with stuff)

This weapon is very quite. Much more so than I anticipated. It is also far more accurate than I dreamed. I can hit a 2 liter soda bottle at 75 feet with almost flat trajectory when using a modified pocket vortex with about 70 psi. (when i say modified, i simply mean that i cut the ends of the tails and curved them a little)

As the title states, this is a 51mm anti-vehicle weapon for use during paintball or combined milsim. It launches nerf pocket vortex footballs as well as waterballoons or water grenades.

Barrel: 22" of 2" Pressure Rated PVC Pipe

Chamber: 12.5" of 2.5" Pressure Rated PVC Pipe

Valve: 3/4" QEV Bought from McMaster

Range with 34 gram pocket vortex at 70 psi: 560 feet (this was confirmed with google maps)

Other ammo has yet to be tested, as i need to find a decent sabot for the waterballoons.

Image

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The tee before the barrel, was plugged on the back end. The stock is simply a 3/8" X 6" nipple threaded into the plug.

The trigger is actually on a weird slant because I didn't have very much space. It isn't as comfortable as I hoped. The trigger is much to small for my hand.

Overall, this gun is very easy to use. The QEV performs so well, that i have accidently set it off wen my schrader leaked when i disconnected my pump. I hope to eventually get a HPA set up. 10 or 15 continuous shots from this thing would be more than enough to make me happy.
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Unread postAuthor: Mitchza89 » Thu Jul 30, 2009 12:12 am

Definitely a Frankenstein build but you can't argue with results.

Good job mate :)
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Unread postAuthor: POLAND_SPUD » Thu Jul 30, 2009 5:36 am

I am sure you could find a metal chamber of more less the same size (a FE or something)
then you could turn it 180 deg and use it as a stock... if you have a HP pump you can also use a smaller chamber and get more power at the same time...

I suspect that you wouldn't even feel the extra weight as the gun would be better balanced and you wouldn't need the stock you use now

you could also use a shorter nipple between the T and the valve...

with a metal chamber you can use it at 300 psi
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Last edited by POLAND_SPUD on Thu Jul 30, 2009 8:25 am, edited 2 times in total.
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Re: 51mm Anti-Tank

Unread postAuthor: Ragnarok » Thu Jul 30, 2009 6:17 am

A neat little build, but I'm a little surprised you didn't decide to fit any kind of pressure gauge to it, nor any over-pressure pop-off.
I wouldn't be using any kind of HPA (or equally, CO2) in a cannon without that as a safety net - but then again, it is your cannon.

It sounds like a decent performer, which will probably do what you need it to do.

Like Poland_Spud suggests, if you can find a way to rotate the chamber 180, that would also be a fix for the awkward grip angle.

~~~~~

Just as a closing heads-up, it's good practise to avoid using the word weapon - it's a word with all kind of negative connotations that spudding doesn't need to be lumbered with.

(The eagle-eyed may have noticed it's very rare to see me personally talking about them as "guns" either. I usually only talk about launchers, cannons or spudguns - for various reasons.)
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Does that thing kinda look like a big cat to you?
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Unread postAuthor: dewey-1 » Thu Jul 30, 2009 9:59 am

POLAND_SPUD wrote:I am sure you could find a metal chamber of more less the same size (a FE or something)
then you could turn it 180 deg and use it as a stock... if you have a HP pump you can also use a smaller chamber and get more power at the same time...

I suspect that you wouldn't even feel the extra weight as the gun would be better balanced and you wouldn't need the stock you use now

you could also use a shorter nipple between the T and the valve...

with a metal chamber you can use it at 300 psi


A variation of what POLAND SPUD is referring to can be seen here;

http://www.spudfiles.com/forums/asco-ne ... 17764.html

@deathofall; Could you please post the GGDT screen print of your launcher's specifications?

I am curious to see your results verses GGDT predictions.

Also please post a picture of; "when i say modified, i simply mean that i cut the ends of the tails and curved them a little)"

Nice clean build and good performance!
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Unread postAuthor: jackssmirkingrevenge » Thu Jul 30, 2009 10:01 am

Wouldn't this configuration have been better? You would have had the blowgun in a more conveinient position, as well as eliminating the dead space between the valve and the barrel.
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Unread postAuthor: POLAND_SPUD » Thu Jul 30, 2009 11:32 am

well I am not saying that it would be an ideal solution... but it would be the easiest one to implement... jack's design is good but the centre of mass would be shifted forward.. especially if you decide to switch to metal...

ASCO launcher is good as far as performance is concerned as it has the same number of bends...

it's really all about the chamber lenght... if the chamber you use is short (25-30 cm) then the design I proposed is better as the trigger would be in optimal position... with longer chamber (that is 30 - 50 cm) the one used on ASCO nerf launcher would be more ergonomic
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Last edited by POLAND_SPUD on Thu Jul 30, 2009 12:38 pm, edited 1 time in total.
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Unread postAuthor: thedeathofall » Thu Jul 30, 2009 12:38 pm

Well thanks for all the comments. I was pretty surprised when I logged on this morning to see everyone here.

As i (think) i stated in the beginning, I am not finished with this yet. I would have added a pressure gauge or pop off, but because I don't have Co2 or HPA (yet) and I also broke my gauge, I didn't find it necessary.

I am still looking for the best design. I think I may try jacks configuration.

@Dewey,

What really surprised me was that GGDT predicted far less power and distance.

Image

As you can see by the screen shot, It was predicting less than 200 FPS and less than 300 feet distance. I can barely see the nerf when it exits the muzzle at 70 psi, meaning that it is traveling almost 300 FOPS and it doubled its predicted range. I didn't even have the correct drag coefficient typed in.

For the modification of the pocket vortexes, I simply cut the last 1/4 inch and superglued it on at a different angle. You cant really tell in the picture, but i did this to all three fins. This actually increases drag, but it is the most accurate ammo i have ever shot.

Image
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Unread postAuthor: POLAND_SPUD » Thu Jul 30, 2009 12:53 pm

you'll get a huge performance increase if you used higher pressures and for that you'll need a metal chamber
even if you cut its size by a factor of 2 you would rather have the whole mass more ballanced so IMHO try one with the chamber used as the stock

check the data you've entered into GGDT... AFAIK 0.5oz is rougly 28g.. I doubt that the piston is so heavy as the one on my 'european' 1/2" QEV is less than 5g

most guys model QEVs as generic valves with 5ms opening time and dweel time of 1000... also 60% for flow coef seems too optimistic as 65% is the max flow you can get (enter something like 45%)

also I suspect that a nerf dart has a better cd value than 0.5... I am not an expert here as I've never even seen one let alone shoot one but that's my guess (ask btrettel IIRC he has done some research)

and finally, don't judge the guns performance by what you can see when you shoot it... people are no good at guessing dimmenisons, distance or velocities of stuff
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Unread postAuthor: thedeathofall » Thu Jul 30, 2009 1:02 pm

As great as high pressure sounds, it isnt realistic for me. I dont have a high pressure pump, C02 or HPA. I doubt i will buy it anytime soon as i am leaving for school in a month.

Secondly, I dont want that much more performance. This thing is sending a foam rocket through 6 layers of cardboard and denting the drywall in my garage. I dont want to kill anyone on the field if this thing missfires. so adding 6 lbs of weight for a metal chamber, is unrealistic. Remember, I havent taken this thing above 80 psi. Who knows what it will do at 100 or 120 psi.

Thanks for the info about GGDT though
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Unread postAuthor: cannon monkey » Thu Jul 30, 2009 1:14 pm

for water ballons cut a dixie cup... 4 cuts down the side spaded out even basicly one at 12 oclock 3 6 and 9 oclock :) hope that helps...o and dont take it above 40 psi
in the 40 + range they break in the barrel just giving you a warning
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Unread postAuthor: thedeathofall » Thu Jul 30, 2009 1:21 pm

thanks for the heads up. I was thinking about dixie cups. I will probably try them.
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Unread postAuthor: dewey-1 » Thu Jul 30, 2009 1:21 pm

thedeathofall wrote:What really surprised me was that GGDT predicted far less power and distance.


Thanks for the information!
I too was questioning the GGDT predictions on my ASCO launcher.
The results I got were 380 feet at 28 degrees with 447fps velocity.

And this is with 1.5 inch valve, 30 inch barrel and 185 cu in chamber.
So hopefully I can get results higher like you did.

Are you using sabot/wadding with the Nerfs?

A few hints;
Try a 2.5" closed cell foam stress ball as wadding. It helps immensely! It also protects the fins from the initial air blast.
I also spray teflon mold release on the stress ball and Nerf. Reduces any friction. It is surprising how rough sch40 PVC pipe is on the inside.
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Unread postAuthor: thedeathofall » Thu Jul 30, 2009 2:34 pm

no problem Dewey! thanks for the tip. I am not currently using any sabot with my nerfs. They are a really close fit. I have to trim the tails a little so that it will slide down. It still takes almost 5 seconds for the vortex to slide to the base of the barrel.

I redesigned this thing again. Now it looks like jacks drawing but without the stock. I decided that the stock is not worth it. I may eventually come up with something, but not right now.

I also weighed it; 5 lbs 14 ounces. This is pretty light, especially for an ainti vehicle weapon. It is also compact enough for me to stuff in a backpack and carry around when i am playing a game. I will just remove it from the pack, and take out the enemy when i need to.
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Unread postAuthor: randompkguy » Fri Jul 31, 2009 12:11 am

can the mcmaster qev he is using take high pressures? it says it is only rated to 125 on the site. i only ask b/c I use the same valve as a pilot on my metal cannon, and want to know how high I can take it
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