I have a question, what would make a good charge for the projectile in the tennis ball? say if you wanted to make a charge for when it hits somthing. like taping some strikers from a matchbox inside the ball and some match heads close to it and filled it with some sort of explosive?

thats what i was thinking. why would you want to send a tennis ball into the air? theres no fun in that lol.i seen one of my friends try to make a Halo Plasma Grenade, he used a Styerophoam ball and put matches in it with lighter fluid, and some axe, light it and throw FAST it was pretty cool, but burned his hand lol so worth it

keep it simple for your first time, use something like BP
but when you get some experience you can experiment

i've built a multi purpose lancher made from welded box steel
and a 40mm barrel.

it will launch potatoes 400-500 meters

however i've built purpose made shells out fo spun cardboard tubing
then i use a cap from a shotgun shell to detonate a secondary charge on impact.
although it only works when u fire it as a mortar and it comes down straight.

great fun to make and use if you have a welder and come spare steel...

This was just meant to be a short physics period blow-off (insert drum riff) but i just realized my pipe was too small for the tennis balls. Back to the drawing board.

...shouldn't that have been step one?

i made a potato/tennis ball launcher out of steel powered by propane it gets hot quick tho its all electric after 50lb of pressure is reached in the chamber it is ign. and the ball valve opens and bang lol tried it with pvc the first time blew apart then i thought of using alum. but i couldnt weld alum. so i used steel tube works like a charm and its super loud too sounds like a canon kicks like a canon too

Good restraint would be?

i really dont know what your asking but if your asking how its restrained its welded on a rotating platform with metal t-post weld at all four corners t-posts are drove in ground all the way except 4 in. still pulls the front up and drives the back down alittle my buddy decided to stand on the front of it once to try and keep it from jumping and it bounced him up and made apple sauce on the back of his head he did a complete frontflip and landed on his face i bout shit myself i thouht i killed him just stuned him for about 5 mins and his head hurt for days he wanted to go to the er but his dad said he was a pussy just tough it out it was his own fault for being a fuck head im thinking bout welding it to my trailer have to cut about 2 in. off the front or back of platform then it would be portable i dont know i think it would jump too much

Interesting....I'll look into some good design ideas, but ill keep yours upfront

i made a tennis ball mortar a few years back. a few pringles cans, some pvc and a thing of staight/zippo fuel. it works pretty well i guess. idk got the idea from a book called backyard ballistics.