I know how you did it, and I also know why. What I'm trying to point out is that you're exceeding the limitations on how well the engine can compute collisions - the point at which your shots will no longer work. However, you're right; a lifetime of .02 seconds is roughly equivalent to the 50 FPS average you're probably getting out of the game and, barring that, your monitor. If you shorten the time to, say, .01 seconds, the game isn't making physics calculations in that time frame so by the time it gets around to calculating its final position the projectile is no longer in play. It's an implimentation limitation, and really there's not a good way to make things "more" precise.