spring piston.

[mouz]

has anyone else here made a spring piston?!?!?!? they are easy to build and need no pumping. down side: calibers higher that 30 probably aren't going to work well at all. i just built one, and it works!!! its .176 cal, a BB is just a tiny bit loose in the type of tube the barrel is made of, a BB being .175 cal. i don't have any BB's right now though, so iv'e been shooting tiny pieces of aluminum foil: http://www.flickr.com/photos/49702362@N04/4838976809/
here is the gun: http://www.flickr.com/photos/49702362@N04/4839586830/in/photostream/

here is the plunger: http://www.flickr.com/photos/49702362@N04/4839594438/in/photostream/
and a close up: http://www.flickr.com/photos/49702362@N04/4839597030/in/photostream/

and the trigger mechanism: http://www.flickr.com/photos/49702362@N04/4838979143/in/photostream/
you simply flick the bolt up and the rubber bands fire it forward propelling the projectile at about 120 fps or so (total guess) it isn't loud at all.

[FighterAce]

I've made something similar but springs... but I was disappointed with the power so I abandoned it.
Nice mechanism 

[mouz]

i think the elastic is more efficient than a metal spring, but it has to be replaced. this gun is about as powerful as a crappy lever action BB gun. i plan to some day make one that is really nice, maybe .25 or .30 cal, with a big powerful spring in it, because the design i'm thinking of wont work with rubber.

[FighterAce]

Try a recoil spring off a rifle  That will give it some serious oomph

[boar]

stu was messing with something liks this a while back with the rubbers you can use multiples and cock them 1 at a time i think its interesting and would like to see where it ends up it would be cool to go afeild without a pump

Boar

[mouz]

i just rifled the barrel, it has no sights, but i think it increased accuracy a TON.