SMG-style launcher.... plans only

[cyanite]

Hey People

I just designed this yesterday, and it will be my first piston so I've decided to run it by here first before I actually make it... I'm planning on it being under 20 inches long. Any advice (or critisims) would be appreciated.

This gun will be;

Pneumatic (Duh)
Filled from a bike pump (hence the small size)
Single shot
Firing a small ball bearing
Be made from PVC and copper (anyone know how to join these 2 together)
Be actuated by sprinkler valve

Here are the plans:

(Oh, and I need a better place to put the schrader valve... It needs a ball valve so I can take the pump off the gun without losing pressure, ideas?)

[jackssmirkingrevenge]

I think the sprinkler valve is overkill as a pilot valve on a small BB barrel - you will get the same performance either by a) using the sprinker as the main valve or b) exhausting the pilot chamber with the blowgun directly.

[hi]

it'll work, but like jack said, the sprinkler is overkill. infact you piston may go into the sprinkler valve, unless its a male adaptor. its going to proform like a normal store bought bb gun, maybe slightly better.

if i were you (which im not) i would build this...

http://www.spudfiles.com/forums/coaxial ... t2122.html

its a slightly different design, but would be more powwerful.

[cyanite]

Ok, thanks guys... Ill be sure to post pics of the launcher when it is done... just need a paint job idea...

Jack: I wanted this launcher to be overkill anyways, I'm salvaging the sprinkler valve off my over-under launcher anyway... and considering the blow gun is epoxied on... The sprinkler valve will be killer for th gun's looks and confort anyway

[jackssmirkingrevenge]

By overkill I mean you will gain no performance advantage over the sprinkler valve if you use a piston, personally in this case ´'d just mound the sprinkler directly.

[cyanite]

I built the cannon around this.... but it sure as hell ain't the 'small smg' I was going for... in fact, this launcher is as big, or bigger than the previous one.
Skhrnykhsk should be posting pics soon...
At the moment, it's not working too well (if at all).

Sometimes the thing works perfectly... most of the time either the sprinkler valve stops working... or the piston wont seal the barrel

The piston ATM is a lynx deodorant can, cut in half, with a 1cm thick foam disc pushed into the open end to seal the barrel. The whole thing is wrapped in tape, and has had about 50 grams of 'BP Energrease' smeared over it.

Also, the bumpers keep getting launched through the back of the chamber, and into the valve.

Any ideas on fixing this?

[mega_swordman]

Is the equalization hole big enough? On paper (your words) I can't really see a problem. Try posting some pictures of the piston and other parts so we may be able to properly help you.

[cyanite]

Ummm, It doesn't have an equalization hole... but the piston is so damn ghetto air gets around it anyway... A BIG problem seems to be that our bike pump ain't filling the area behind the piston fast enough to actually push it firmly onto the barrel.... and is foam (cut from a camping mattress underlay.. its pretty firm/ non-porous) actually strong enough to avoid the barrel getting rammed through it?
Damn I wish I could post pics at the moment, but the launcher is at Skhrnykhsk's place... my parents ain't too supportive of something that can clearly spear someone to something...
I suppose ill try to post tomorrow after school

[paddo]

i think that your biggest problem is the slow speed at which you fill it. if the piston doesn't seal against the chamber walls very well then it will take a burst of pressure quickly to get it to seal against the barrel. otherwise it mite get to the barrel and then not have enough to seal and then leak.
wish i could help more mate.

[cyanite]

Damn.... well thanks for your help all... I might try a small fill chamber with a ball valve to get that piston slammed against that barrel.... [/img]