The flatness of trajectory is dependent upon the muzzle velocity, and, to some extent, upon the form of the bullet. Our bullet is pointed and the muzzle velocity is 2700 feet per second, which is a very high muzzle velocity.
Two rifles of different type may be equally accurate, but the accuracy of the one having the flatter trajectory will, naturally, be less affected by slight errors in sight setting.
Again, another advantage of the rifle with the flatter trajectory is that it holds more ground under its fire. For example, take our service rifle: At a range of 500 yards, the bullet, at the highest point in its trajectory or line of flight, is 2 feet above the line of sight. It is, therefore, apparent that if the bottom of an object 2 feet or greater, is aimed at, it would be struck if it were anywhere under 500 yards. Now, take a rifle with a very curved trajectory, say one whose bullet, at the highest point of the trajectory corresponding to a range of 500 yards, is 10 feet above the line of sight. There will be a large extent of ground between the target and the rifle that is not danger space for a target 2 feet above the line of sight. Hence, we see that the rifle with the flatter trajectory is better.
The continuous danger space afforded by the flat trajectory of our service rifle enables us to adopt a universal sight for all ranges up to 500 yards,—that is, the battle sight, which is the rear sight ready for use when the sight leaf is laid down.
[1411]. Cone of fire or cone of dispersion. If a body of soldiers fire at the same target the bullets will not, of course, follow the same path, but will be scattered. This is due to differences in sights, parts of the rifle, ammunition, and to a greater extent, to the individual errors of the soldiers in aiming and firing.
The trajectories or paths of the bullets considered together form a horn-shaped figure or cone, called the Cone of fire or cone of dispersion. (See [Fig. 44].)
Fig. 44