A blow-forward piston airgun..

[iloveairguns]

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

[jackssmirkingrevenge]

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?

[iloveairguns]

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

[iloveairguns]

yes it has a rod in the piston to push the ammo. well achieving maybe better power and no worry of airtight ammo.

[jackssmirkingrevenge]

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

[Technician1002]

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 ... 21827.html

1/2 inch barrel and AA battery
Before
2.5 inch barrel and sabot
After

[jackssmirkingrevenge]

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][/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.

[iloveairguns]

well i would prolly put rubber in front of the piston to dampen the impact

[jackssmirkingrevenge]

Note how nailguns also feature an air bumper:

[iloveairguns]

well my gun wont be to say the least a spud cannon maybe a large sized bbmg not sure

[iloveairguns]

so umm.. instructions for a sabot airgun maybe? not so familiar with sabot thingy

[Technician1002]

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.

[iloveairguns]

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

[iloveairguns]

yea and the airgun wont be a spud cannon as i have already said, more a rifle or pistol

[jackssmirkingrevenge]

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

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