Trial Shots Or Volleys
If the ground is so dry and dusty that the fall of the bullets is
visible through a glass or with the naked eye, a method of determining
the distance is afforded by using a number of trial shots or volleys.
The method of using trial volleys is as follows: The sights are raised
for the estimated range and one volley is fired. If this appears to hit
but little short of the mark, an increase of elevation of 100 yards will
be used for the next volley. When the object is enclosed between two
volleys, a mean of the elevation will be adopted as the correct range.
The range may be obtained from a near-by battery or machine gun. This is
the best method when available.--Small Arms Firing Manual.