Newbie builder, need some help on a school project

[Potatolauncher424]

Hey potato launchers! (or whatever y'all call each other! XD) I've been researching for a potato gun project at school and need some help. I can't use propellant so just air pressure for now. So far my materials are: Tank (4 in. pvc to 3 in. pvc) Valve (3x3 in.) Barrel (3 in.) Glue/Primer (8 oz each) and Ammo (tennis or racketball.) Please no hate or sarcasm, any help is accepted. I gotta try to beat the record of 250 yards or meters. (I'm American and still have convinced myself they're the same.) I can't use anything but pvc and can't afford an auto in-line valve, just a pvc one. I'm pretty sure that sch. 40 is strong enough because it's able to hold 700 psi. P.S., I only have 1 hour a week at school to work on this, so please no crazy ideas. I'm also not in a financial state to spend more than 50-60 more dollars on this. (I mean, whatcha expect out of a 6th grader?)


Thanks in advance,
Potatolauncher424(Noah if y'all are getting formal.)