1. Gravity acts on a plane that intersects the central axis of the earth and so in effect, if you could plot the strength of gravity on a cross section of the earth, gravity would be illustrated as rings around the earth.
2. Gravity affects everything! Even light, so what we think of as a straight line of sight is actually curved, albeit ever so slighlty.
3. Gravity acts on the mass of an object and not its size. A cardboard box and a rock having the same mass would be acted on equally by gravity.
4. As you move farther away from the center of the earth, the force of gravity becomes less.
If bullets were like rockets and could sustain peak velocities, the could travel much further before hitting the ground, however, they are not and gravity, in conjunction with friction, acts upon the bullet causing it to lose velocity and eventually stop. Likewise, if a bullet were fired in a vacuum, it would retain near peak velocity and travel much farther before stopping.
I think one could assume that a bullet fired on a line of sight parallel to the earth's surface would have a higher amount (over time) of gravitational forces applied to it than a bullet fired on a path perpendicular (sp) to the earth's surface, and being such would travel a slightly shorter distance within a measured time frame (may be fractional). Assuming that this is true, a bullet fired on a horizontal path would have slightly less gravitational forces acting on it producing an altered flight path.
Bclark1 is any of this making sense to you? It works out in my head!