Hi! I have been trying to figure out this problem for hours now. If I want two bullets discharging from the same rifle to collide in midair with just a change in the angle of elevation. Can you show the time interval needed? I think that this question is interesting enough to be posted. Thanks. According to the rules of the forum I will post my own attempts to solve this problem. What I have done so far is write down the projectile motion equations, say that their final position must be equal for a collision to happen and of course the acceleration vectors. These does not seem to be enough. Any suggestions would be appreciated.