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A blow-forward piston airgun..

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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A blow-forward piston airgun..

Unread postAuthor: iloveairguns » Tue Dec 18, 2012 3:58 pm

So need help with this design, which uses a blow forward piston like nailguns. i need info on the valve and how to make the best possible piston.. :help: help help help
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so here are some gun part descriptions: the piston is hollow but sealed of course from the another end, and it doesnt yet have the ramming rod (the long thingy in middle of piston)
airgunplan.png (4.79 KiB) Viewed 1452 times
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Unread postAuthor: jackssmirkingrevenge » Tue Dec 18, 2012 4:03 pm

So the piston will have a rod physically pushing the projectile?

The first question is, what are you hoping to achieve that you couldn't with a conventional setup?
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Unread postAuthor: iloveairguns » Tue Dec 18, 2012 4:08 pm

hey and the valve will be at the back of the gun, it offers optimal flow and easiest to build there. maybe a poppet valve, piston valve :idea:
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Unread postAuthor: iloveairguns » Tue Dec 18, 2012 4:09 pm

yes it has a rod in the piston to push the ammo. well achieving maybe better power and no worry of airtight ammo.
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Unread postAuthor: jackssmirkingrevenge » Tue Dec 18, 2012 4:56 pm

iloveairguns wrote:well achieving maybe better power and no worry of airtight ammo.


Some things to consider:

- the piston has a bigger surface area, so that does provide you with more potential power, but you're also having to push the weight of a relatively heavy piston, so that advantage is lost

- you have to stop that piston, which puts a lot of stress on your system and also eats away at the performance.

It's a good idea if you want to launch a heavy projectile at relatively slow speeds, like for example a ballistic knife, but for a BB, not a terribly good idea.

Instead of a piston with a push rod, you can just have the piston itself as a sabot.

Have a look at Btb's go: http://www.spudfiles.com/forums/silent- ... 19729.html
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Unread postAuthor: Technician1002 » Tue Dec 18, 2012 6:39 pm

this thread shows the advantage of a large diameter barrel and sabot on small diameter projectiles. In this case AA batteries launched from a 2.5 inch barrel and directly comparing damage to the battery.
http://www.spudfiles.com/forums/flat-aa-battery-i-challenge-some1-to-replicate-this-video-t21827.html

1/2 inch barrel and AA battery
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2.5 inch barrel and sabot
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Unread postAuthor: jackssmirkingrevenge » Tue Dec 18, 2012 7:14 pm

Technician1002 wrote:this thread shows the advantage of a large diameter barrel and sabot on small diameter projectiles.


This applies to the "typical" sabot round setup, involving a small dense projectile in a large lightweight sabot.

[youtube]http://www.youtube.com/watch?v=0giK-zqrAKI[/youtube]

This gives a large area and low density in the barrel, giving good acceleration, then once the sub projectile is separated from the sabot it has a small area and high density, meaning it will retain its velocity for longer.

In the "nailgun style" setup however, the piston/sabot would tend to be heavier because it needs to survive the impact and be arrested, therefore negating the advantages to a large extent.
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Unread postAuthor: iloveairguns » Wed Dec 19, 2012 7:16 am

well i would prolly put rubber in front of the piston to dampen the impact
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Unread postAuthor: jackssmirkingrevenge » Wed Dec 19, 2012 7:31 am

Note how nailguns also feature an air bumper:

Image
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Unread postAuthor: iloveairguns » Wed Dec 19, 2012 8:30 am

well my gun wont be to say the least a spud cannon maybe a large sized bbmg not sure
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Unread postAuthor: iloveairguns » Thu Dec 20, 2012 4:36 pm

so umm.. instructions for a sabot airgun maybe? not so familiar with sabot thingy :roll:
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Unread postAuthor: Technician1002 » Fri Dec 21, 2012 2:15 am

Sabot means wooden shoe. It is a large container for a small projectile.

My battery sabot is the bottom from a plastic bottle. A swim noodle foam ring is just to center the round for launch.

Image[url][/url]
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Unread postAuthor: iloveairguns » Fri Dec 21, 2012 2:34 am

but i dont really want to see your thingy but get some directions for the airgun and the valve and materials i need urgent help with the things i listed, airgun construction, the valve, materials. help with these :?
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Unread postAuthor: iloveairguns » Fri Dec 21, 2012 2:35 am

yea and the airgun wont be a spud cannon as i have already said, more a rifle or pistol
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Unread postAuthor: jackssmirkingrevenge » Fri Dec 21, 2012 3:00 am

http://www.spudfiles.com/forums/copper- ... 24060.html

A simple QEV launcher would be a good basis to start off with.
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