Well, if you don't take the effect of drag into account, and assume the force of gravity to be constant at 9.8m/s^2, then a bullet fired at 800m/s straight up would reach a max altitude of roughly 16,327m in 40.8 seconds. Total flight time is roughly 82 seconds.

If you have a graphing calculator (Texas Instruments TI-83 or similar) you can use the following parametric function to calculate the trajectory of a projectile sans drag(make sure the calculator is in degree and parametric graph modes). I do not (yet) know the function(s) necessary for accurately calculating the effect of drag on the bullet. I haven't gotten that far in calculus yet.

X(t)=(velocity in m/s)t*cos (launch angle in degrees)
Y(t)=(velocity in m/s)t*sin (launch angle in degrees) - 9.8t^2

So the functions I used for your calculation are:

X(t)=0 (because there is no horizontal component of velocity)
Y(t)=800t*sin 90 - 9.8t^2

Mike