ROCK SOLID wrote:My neighbour also has a spud gun and he said he can send a tennis ball over a mile.
Jack has it in one. This is practically impossible, and your neighbour is spouting pseudoscience.
Filling a tennis ball with butane will not improve it's range. More likely, as it removes the pressurization of the ball in the first place, making it spongy, it will actually lose range.
Now, if you add some weight to the ball, by injecting it with water instead, that might help range, but no way is a mile possible with anything that can be practically built in a back garden.
I've not heard a report of more than around 500 metres range with an un-optimised projectile that I would believe, and normally, unless it was a seriously big-shot member that had claimed it, I would probably doubt claims of more than a 1/4 mile.
In this case, you have to ask how is he supposed to know it's gone a mile in the first place. He went out there and found it again? Hardly likely.
Nor could he watch it out there, then make an accurate range guess - at that distance, a tennis ball makes up only 0.15 of a minute of arc, which is like you being able to identify a small pea at 200 yards.
Get a demonstration.The ball probably won't go more than 200-300 yards, tops.
In this hobby, it's worth knowing that most people, unless they've had a lot of practise, will drastically overestimate range. Now, I've done calculations, and I know that with the right low drag projectile, I could
almost certainly beat one mile range with some of my launchers, but I'd have one heck of a time proving it beyond all doubt.
What I ask is - do you need so much range? If you're firing that far, then you're probably firing out of your visual range, and that's potentially VERY dangerous. I won't fire anything unless I have a very good idea of where it's going to end up, and I know that area, and several radii out from there are going to be clear of innocent bystanders both for some time before and after firing.
The other thing is, it won't be much fun. The projectile will have to travel so fast you won't be able to see it's flight, and impact won't be visible - and that's not particularly entertaining.
and i asked how he did this 
