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1/2 inch bore metal cannon build

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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1/2 inch bore metal cannon build

Unread postAuthor: High-PSI » Thu May 19, 2011 8:46 pm

Hey guys,

Here are some preliminary pics of a 1/2 inch bore (.600") cannon. The tank is made of 3 inch ID 1/8 inch wall DOM high tensile steel pipe with 1/8 inch steel hemispheres MIG welded to the ends. You can see the one hemisphere has been machined on the lathe along with the pipe nipple to form a good tight seam. That will make the inside transition easier to smooth out once welding is done. It also assures a good straight tank to valve assembly.

The valve is a 1 inch ID Granzow diaphram valve with a CV of 12. It will be piloted by a small trigger valve (I will show that later).

You can see the 1 inch to 1/2 inch reducer that I ported and polished. That was accomplished by spinning it in the lathe and using the old trusty Dremel with various wheels to achieve a very slick surface. The front of the inside of the tank will get the same treatment as will the inside of the valve to remove any flashing and smooth flow.

This gun will run 300 psi (310 psi is the limit of my compressor). I will make my own slugs out of Delrin and a few out of steel.

I have a decent muzzle-loader scope I bought a month back and never used. So, that scope will find a home on top of this gun. I also plan on venting the barrel to increase accuracy.

Oh, the barrel will is sch 40 aluminum that is 33 inches long with 3 inches of vented section beyond that. I will be firing slugs as light as 7 grams and as heavy as 35 grams.

I will keep pictures coming as I have them.

Matt
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Unread postAuthor: daniel0663 » Thu May 19, 2011 10:47 pm

Yeah man looks promising.
mmm wish i had a lathe :roll:
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Unread postAuthor: warhead052 » Fri May 20, 2011 9:33 am

Looks nice. Did you make those threads your self?
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Unread postAuthor: jackssmirkingrevenge » Fri May 20, 2011 11:05 am

Looking great as always, and dammit now all lathe related stuff is looking fapworthy!

While it only uses 10% of the chamber pressure, it should put commercially available 50 cal airguns like the Dragon Slayer to shame, albeit with just one shot per fill.
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Unread postAuthor: High-PSI » Fri May 20, 2011 1:47 pm

That fitting is a basic black steel reducer. I merely ported and polished it.

So, why are the high pressure airguns relatively low power (compared to this)?

Anyway, thanks for the kind words. I am doing my best to build the best guns I can with what I have. Unfortunately, most of what I know is related to these same valves. I do not have the time to develop my own fast acting valve. So, I use these. Besides, as long as I over spec the bore size of the valve and choke it down to a smaller bore barrel, the loss through valve restriction should be minimized.

I am off to the shop to do some welding!

Matt
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Unread postAuthor: jackssmirkingrevenge » Fri May 20, 2011 4:00 pm

High-PSI wrote:So, why are the high pressure airguns relatively low power (compared to this)?


They have hammer valves which only allow a short burst of air though relatively restrictive flow. Yours on the otherhand dumps a substantial chamber through a fast valve with better flow than the barrel.
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Unread postAuthor: urgle the danish cow » Fri May 20, 2011 4:00 pm

jackssmirkingrevenge wrote:Looking great as always, and dammit now all lathe related stuff is looking fapworthy!

While it only uses 10% of the chamber pressure, it should put commercially available 50 cal airguns like the Dragon Slayer to shame, albeit with just one shot per fill.


but note that those put out some 230 ft/lbs with minimal shots
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Unread postAuthor: velocity3x » Fri May 20, 2011 6:37 pm

Matt,
Extremely nice work on the tank!


High-PSI wrote:So, why are the high pressure airguns relatively low power (compared to this)?

I think that's a matter of perspective. :lol:

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Unread postAuthor: High-PSI » Fri May 27, 2011 3:13 pm

Hey Guys,

Since I cannot get GGDT to run (bummer), can anyone give me some numbers on this?

My barrel is .600 inch ID, 36 inches long, the valve CV is 14, and I am looking into using a paintball tank to charge the primary tank to 500 psi. The tank to barrel ratio will be 1 to 1. The slug should weigh 10 grams.

What would my muzzle velocity be? If I fired a 40 gram slug, what would my muzzle energy be?

Thanks!

Matt
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Unread postAuthor: saefroch » Fri May 27, 2011 8:25 pm

Knowing the diameter and mass of your diaphragm and the pilot volume and port size would be nice...

Preliminary estimates: 680fps and 162.5ft/lbs, or with the heavier slug 370fps and 194.7ft/lbs
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Unread postAuthor: High-PSI » Fri May 27, 2011 9:24 pm

Cool, thanks.

The diameter of the diaphram is 1.875 inches. It weighs 37 grams.

Hmm, I have have assumed at 500 PSI the muzzle velocity would be much higher.

Anyway, there is only one way to verify this------ BUILD IT! :twisted:
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Unread postAuthor: saefroch » Fri May 27, 2011 9:31 pm

Not much of a change in the predictions, but from what I've been getting back, it seems you haven't run GGDT for this build before... I'm getting a "Barrel choking flow" warning. My simulation of your heavily modified sprinkler valve may be off, but even so, you should consider a larger barrel.
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Unread postAuthor: Gippeto » Fri May 27, 2011 10:42 pm

jackssmirkingrevenge wrote:
High-PSI wrote:So, why are the high pressure airguns relatively low power (compared to this)?


They have hammer valves which only allow a short burst of air though relatively restrictive flow. Yours on the otherhand dumps a substantial chamber through a fast valve with better flow than the barrel.


Yeah, hammer valves SUCK!

Oh...wait a second...mayhap NOT! :D

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Unread postAuthor: jackssmirkingrevenge » Sat May 28, 2011 1:22 am

saefroch wrote:I'm getting a "Barrel choking flow" warning.


This means valve flow is already as good as it can be for the given barrel diameter - understandable given the disparity in sizes.

Yeah, hammer valves SUCK!


... so much that you only used one as a pilot valve ;)

My point, which in no way I imagined would have been contentious, was that for a given pressure, a chamber dump through an exhaust valve will give better performance than a burst of air from a hammer valve.
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Unread postAuthor: High-PSI » Sat May 28, 2011 6:57 am

Hmm, since deciding to go with a paintball tank for pressurization, I may as well test my chamber for 1,000 PSI. It is, after all, 3 inch diameter 1/8 inch wall DOM tube. I think I will hydro test it to about 2,000 PSI to make sure it will handle extremely high pressure and do some serious velocity testing! I know these valves (the bigger 2 inch version) are being used in 800 psi applications.

I bet I could see 1,000 FPS with a super light slug and that much pressure......

Anyway, I know, for sure, it will handle 500 psi without a problem.

I still plan on testing the tank, though. That is easy enough to do.

I can, also to with a 3/4 inch barrel. I think the valve flow would still be good enough for that. But, I think the recoil would be pretty high at that diameter with high pressure.

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