projectile motion...?

to change speed
get a fixed slope with flat end to it then change release point on the slope - this will alter end velocity

to change angle of slope
get a fixed slope with an adjustable end - will need a protractor attached to it. sometimes this is done with a curved (fixed) slope which you can swivel - creating different release angles. but when this is done it is difficult to keep release height the same

remeber to only change one of these things though

Even though most TV shows and movies portray the study of the striations on a slug of a bullet as being ballistics, this is just a modern definition.  Originally it meant the study and calculation of ballistic trajectories.  These calculations, being somewhat complex and time consuming, were the reason and motivation for the development of the first "modern" electronic computer by the US military.  They needed to know how to aim artillery guns to make the shells impact where they wanted.  It was called the Univac and took up enough space to fill up a small house.
If the charge amount [the blackpowder] stays the same, then raising the angle of release will shorten the distance to impact and lowering will extend it to a point.  Of course, lowering too much means you're going to explode the ground right in front of the gun. That would ba a bad thing. The optimal firing angle for optimal effective range is 45 degrees; just ask any shot-put thrower.
However, most modern artillery guns [landbased --to include tanks too -- and naval] can use different amounts of charge.  Of course, the more powder, the higher the muzzle velocity of the projectile.  The higher the muzzle velocity, the more momentum and farther range it will achieve.
Lastly, the shape of the projectile and its aerodynamic properties are also a factor in determining its trajectory.
If you really want to sit and figure out all the necessary calculations, go ahead.  But, that spotter or Forward Observer more than likely doesn't want to wait on the arty guys to break out the pen and paper and would rather let the targetting computer do it.  They did a call for fire now cause they want rounds impacting the target area now.

First.  you always always always split the problem into two parts.   horizontal motion and verticle motion.

Second, velocity needs to be broken down into horizontal and verticle velocity components and depends on the angle.  

Third, the time the object travels horizontally always = time the object travels vertically.  

Fourth, use equations of motion to solve problems.
The applicable equations can be found here...
http://en.wikipedia.org/wiki/Equation_of_motion

overall,

for horizontal motion, v = d/t so that t = d/v

for verticle motion, y = vot + 1/2 at^2
and by substitution,

y = vo x d/v + 1/2 a d^2/v^2

which is in general form

A x^2 + B x + C = y

which is a parabola.  ie.  projectiles travel in parabolic flights.

its easy just look up on the website how stuff work and they got it all written for you.. just try relating the stuff to back to projectile motion