Slavage,
The "jump from the muzzle" is derived from a common misconception that a bullet rises as it leaves the muzzle. In fact, a bullet, as all projectiles travelling horizontally on Earth, begins to fall as soon as it leaves the muzzle. This rate of fall is purely a function of mass and shape and has NOTHING to do with forward motion. The bullet would fall at exactly the same rate from a straight line down the barrel of your gun as it would if you simply dropped it from the muzzle. So the "arc" we all know of as the bullet trajectory is a curve that continues downward at an increasing rate.
Why does the trajectory of a bullet appear to "jump", or go upward, at the beginning of the trajectory? Because the line of sight of your sights or scope is not exactly aligned with the line down the center of your barrel. The sight line is tilted slightly downward, so that it crosses the bullet trajectory. The further downward it is adjusted, the "higher" the bullet appears to "rise" in a trajectory.
Hope that wasn't too technical, but I thought it needed to be clarified.
