Simple. The answer is speed.
A bullet's velocity at the muzzle depends on many factors: propellant, case load, bullet mass, barrel length and barrel friction, to name just a few. Everybody knows this.
But wait!
In a constant gravitational field -- such as exists at your shooting range, and anywhere else on the surface of the Earth for that matter -- bullets follow a parabolic trajectory toward their target. An arc, in other words. Gunmakers know this.
Now speed has the uncanny ability to scale the arc up. The higher the speed, the "flatter" the trajectory (that is, the shorter the parabolic segment). And the flatter the trajectory, the closer the POA and POI are likely to be.
If you really want a straight trajectory, then get as far away as you can from the Earth, Moon, Sun and planets. Even then, the bullet will follow an eccentric path about the Milky Way.
Not an expert here, but physics I, II and III were on my college curriculum.