Archer
The Archery Library
Old Archery Books, Articles and Prints
homebooksarticlesprintsnews
Home > Books > Archery: The Technical Side >
A Study of Points of Aim
Part 5 of 5

Now let use see what further information is to be gained from the curves of sight settings. The vertical line (not drawn in Plate I) at plus 4 millimeters intersects the curves at points which give the ranges, at the different velocities, for which the arrow itself would be aimed on the gold; in other words, the point-blank ranges. The portions of the curves to the right of this line represent sight settings above the arrow, for aiming on the gold. The portions to the left, for the longer ranges, represent sight settings below the arrow, hence physically impossible. But they tell us how far below the arrow the sight would have to be set, if it could be done that way. The information is valuable because it enables us to determine with certainty how strong a prism to use—if we desire to employ this useful aid in long-range shooting—in order to bring our sighting point back on the gold. In the prism sight which I have designed and am using with great success, it is inadvisable to set it nearer the arrow than plus 20 millimeters. For my "dimensions," one prism diopter corresponds to 6.8 millimeters on the scale of the sight. Thus I find, for example, that if I wish to shoot a 400 grain, 160 feet-per-second arrow at 100 yards, 1 must use a prism of at least 5.3 diopters. The next standard prism power being 6 diopters, I find that this prism would be set at 6x6.8 mm. or 40.8 mm. above the 100 yard setting indicated by the curve (minus 16 mm.), or at plus 24.8 mm.

TABLE II. Settings in Millimeters of Sighting Point Relative to Axis of Arrow, for Various Ranges and Velocities.

Arrow
Velocity,
f.p.s.
(a) 325-Grain Arrow
Range in Yards
30 40 50 60 80 100
130 85 60 33 4 —63 —145
140 94 73 50 26 —30 — 93
150 101 81 63 43 — 2 — 53
160 108 90 74 57 + 19 — 25
170 112 97 82 67 34 — 2
180 116 103 90 76 47 + 16
(b) 400-Grain Arrow
130 86 61 35 9 —51 —126
140 95 74 52 29 —20 — 78
150 102 84 64 45 + 5 — 41
160 108 91 75 59 23 — 16
170 112 97 82 68 38 + 5
180 116 103 90 77 50 22

The bold-face figures represent settings for which a prism sight, to bring the actual settings to 20 mm. or higher, would prove useful.

The use of curves and tables like those given will afford the archer more exact knowledge of points of aim and sights, and should therefore be helpful in enabling him to arrive at proper distances and settings for the various ranges with much greater certainty, and much less experimenting, than by the cut-and-try method.