The axis of the bore of the rifle is, say, approximately one inch below the line of sight. The projectile in its ascending curve must cross this line, the distance of which from the muzzle may be readily computed by the preceding formulae, 28b, 26, 27 or 24. The danger zone of the head of the squirrel or grouse lies on either side of the intersection of the ascending curve and the line of sight and extends from 50 to 75 feet more or less from the muzzle of the rifle.

Since in shooting up or down hill gravity acts at an acute angle to the line of sight, its influence upon the height of the inclined trajectory is less than on a horizontal trajectory over the same range, as a result of which for the same elevation of sights the height of the inclined trajectory is greater than that of horizontal trajectory.

For illustration, if the .30-150-2700-.389 is point blank for 200 yards horizontal, the height of the horizontal trajectory is 2.88 inches; at an angle of 60 degrees its point blank range is approximately 400 yards the height of which is approximately 7 inches, and at 100 yards the height of the same inclined trajectory is about 4 inches. In shooting vertically the deviation of the same projectile at 100 yards is 5.4 inches.

With same sights the inclined danger zone is less than the horizontal danger zone, varying inversely as the angle of inclination increases. In the above illustration the horizontal danger zone is continuous for 240 yards; while at an angle of 60 degrees the danger zone is discontinuous, in the as

cending curve its length is approximately 70 yards, and in its descending curve over 50 yards, leaving a space of, say 275 yards, in the trajectory lying without the danger zone.

In inclined shooting hold under or over. See chapter XV.

CHAPTER X.

The Influence of Barometric Pressure, Altitude, Temperature and Humidity Upon the Ballistics of a Projectile.

IT

T is the experience of almost every hunter, lthough a good marksman, who has gone after game in the mountains, to be chagrined at the misses made, losing a large animal or a record head, with no apparent reason for the irregularity in his shooting. Generally, he reasons that the misses were due to over excitement or to the exhaustion of the climb or to both, which causes may have been real factors, but only a part of the sum total of factors that made him score the misses, for after the hunter has regained his mental and physical equilibrium, the misses occur. And it is not until he has returned home that he discovers the great disturbing factor, that the cause was not in himself but in his rifle or the bullet or in both. And then he reasons correctly, but to discern the cause, determine and apply the principles to overcome the seeming irregularities in his shooting is another problem, the solution of which is easily accomplished and the principles readily applied.

The denser (heavier) the air, the greater the resistance it will offer to the motion of the projectile; and conversely, the less the density (lighter) the less the resistance offered.

The value of the ballistic coefficient, C, is usually

that when the barometer is 30", and the temperature 60 degrees F., the atmosphere 2/3 saturated with moisture. Since C measures the ability of the projectile to overcome the resistance of the atmosphere, and this resistance varies according to the principle in the preceding paragraph, then the value of C must vary for the same conditions. Its value is evidently greater when the resistance is less, and less when the resistance is greater.

The barometer is an instrument used for measuring atmospheric pressure, the variation in the weight of which is due to meteorological conditions, to altitude or to both. Since the variation at a given place is due solely to meteorological conditions, the reading of the barometer should be used for our calculations.

However, should a barometer not be at hand, the following table giving the barometric pressures for the different altitudes, temperature 60 degrees F., will be most helpful. Of course, the variation due to meteorological conditions is not taken into consideration in the table, nor can it be, but the correction made by its use will not be far from being correct, the error being due to meteorological conditions which for hunting purposes are negligible. See close of this chapter. For illustration, the normal barometric pressure at Butte, or Denver, is approximately 24" in normal conditions, but preceding a 3 storm it may drop to 23" or 231⁄2", the effect is almost negligible as compared with that of sea level and a mile high.