Trajectory
johnwill, while you are correct that gravity is always pulling down on the bullet, you could not be more incorrect in saying it never rises after leaving the barrel, at least with reference to the horizontal plane. To prove the point with an extreme example, aim the gun at a 45 degree angle from the horizontal. Obviously the bullet "rises" from the horizontal plane.
You are likely thinking of a bullet fired with the barrel parallel to the ground, or angled downward. In those cases, the bullet will indeed start moving downward upon leaving the barrel.
But remember that the sights are above the bore, so the bullet necessarily starts below the line of sight. If we didn't shoot upward from the bore line, we'd never hit what we were aiming at, since the line of sight is always above the bore line. The sights are set so when the bullet is fired, it _rises_ above the line of sight, starts falling after achieving maximum trajectory, and returns to the line of sight at some point further.
If we take a rifle sighted for, say, 300 yards, the bullet indeed rises to intersect the line of sight some distance away from the muzzle (roughly 50 yards), and arcs to cross back down to the point of impact (300 yards).
johnwill, while you are correct that gravity is always pulling down on the bullet, you could not be more incorrect in saying it never rises after leaving the barrel, at least with reference to the horizontal plane. To prove the point with an extreme example, aim the gun at a 45 degree angle from the horizontal. Obviously the bullet "rises" from the horizontal plane.
You are likely thinking of a bullet fired with the barrel parallel to the ground, or angled downward. In those cases, the bullet will indeed start moving downward upon leaving the barrel.
But remember that the sights are above the bore, so the bullet necessarily starts below the line of sight. If we didn't shoot upward from the bore line, we'd never hit what we were aiming at, since the line of sight is always above the bore line. The sights are set so when the bullet is fired, it _rises_ above the line of sight, starts falling after achieving maximum trajectory, and returns to the line of sight at some point further.
If we take a rifle sighted for, say, 300 yards, the bullet indeed rises to intersect the line of sight some distance away from the muzzle (roughly 50 yards), and arcs to cross back down to the point of impact (300 yards).