SpudFiles

Is it possible to make a gun that can launch ammo (weighing 20gms and 2.5cms in diameter) keeping the dimensions within 30cm x30cm x 30cm???
Please reply........

Sure, but how fast do you want the ammo going when it leaves the gun?

An over and under with a 30cm barrel. Chamber volume two or three (or more) times the barrel volume. So, for a 2.5cm barrel use 5cm pipe for the chamber, that'll give you a ~4:1 ratio assuming the chamber and barrel are the same length.

To maximize the barrel length, put the valve on the chamber then a 180° bend to the barrel. Gives you more dead volume behind the ammo but avoids using up a significant amount of the 30cm length limit which is really needed for the barrel.

Fiddle with GGDT to see what appears to be more important; minimizing dead volume or maximizing barrel length. (I would guess that maximizing barrel length is more important.)

Could do a coaxial design but a barrel sealing valve will use up a fair amount of your 30cm length limit.

You could make something like this design using a 3" pipe for the chamber and 1" pipe for the barrel, and use relatively high pressure (say close to 200 psi) and you'd get decent performance (and a LOT of noise )

If you don't want the trouble of making your own piston and want to use standard parts, there's some good inspiration here.

Using those dimensions and atmospheric air at 120 psi, you could use an 8" long, 10" diameter chamber, followed by a 180 degree bend, a 4" burst disk valve, and an 8" long, 4" calibre barrel. That would give you over 800 ft/lbs of muzzle energy with a 450 gram projectile, which is fairly decent in my opinion, and it fits well within the given specs. You might need hearing protection to fire it though...

The speed should be sufficient enough to make the marble penetrate a model township made of cardboard from 2-3m away......

hehe are you planning on destroying someone's history project

all you need is some 1 inch internal diameter pipe for both barrel and chamber and a ball valve.

here's the problem statement for the competition-
Construct a mechanism to fire (project) the specified ball and cause as much destruction as possible to an artificially designed township.

Problem Description

* The built mechanism will be tested for its accuracy and range (power) in an arena made to resemble a small township.
* The dimension of the township will be 2 m × 1.5 m
* The township will have building of many kinds and sizes.
* Points will be awarded for striking the building erected in different parts of the township.
* The smaller and farther the target, higher will be the weightage.
* The ball will be a marble approximately weighing 20 grams.
* The ball will be of diameter 2.5 cm and will be provided to each team

Rules and Regulations

* Each team will consist of a maximum of 3 members.
* Each team will be given three rounds to fire both in the elimination and final round.
* The minimum distance from which the ball can be fired is 2 meters and is compulsory to start with. Thereafter the point of projection is completely the discretion of the participant.
* Extra points will be awarded for striking the target from a longer distance.
* A one touch release mechanism has to be devised for firing the ball.
* Use of hazardous chemicals and explosives will lead to disqualification of the team.
* The mechanism must fit into a box of 30 cm × 30 cm × 30 cm

so can anyone tell me what should be the dimensions of the piston????