Elevation. As previously explained, raising the rear sight increases the range of the bullet and lowering it decreases the range.
The amount of change which a given amount of elevation will cause in the point struck varies with the range and with the rifle and with the ammunition used.
For example, generally and approximately, in order, at a range of 500 yards, to change the point struck 1 foot, the rear sight must be changed 48 yards, while to change the point struck 1 foot at 1000 yards it must be changed 12 yards. That is to say, if you fired a shot at 300 yards, and then with the same aim, hold and other conditions as before, you raised your rear sight 48 yards, the next shot would strike the target 1 foot above the first one, and if you lowered the rear sight 48 yards, the bullet would then strike the target 1 foot below the first one. If firing at 1000 yards, raising the rear sight 12 yards would cause the bullet to strike the target 1 foot higher and lowering the rear sight 12 yards would cause it to strike 1 foot lower.
The following table gives the approximate changes in the rear sight to move the point struck 1 foot at ranges from 100 to 1000 yards:
| Range | Correction in elevation necessary to change the point struck 1 foot |
|---|---|
| 100 | 415 |
| 200 | 185 |
| 300 | 105 |
| 400 | 70 |
| 500 | 48 |
| 600 | 35 |
| 700 | 25 |
| 800 | 20 |
| 900 | 15 |
| 1,000 | 12 |
The score-books issued by the Ordnance Department contain elevation charts and all you have to do is to consult the chart of your score-book in order to get the amount of elevation necessary at any particular range in order to raise or lower your shots any desired distance.
[1384]. Deflection (windage). Corrections in the deflection (side movement) of the bullet are made by means of the windage screw that moves the movable base, each division of the graduations on the rear end of the movable base being called a "point of windage."
One point of windage moves the point struck 4 inches for each 100 yards of range.
That is to say, at 100 yards, 1 point of windage moves the point struck 4 inches; at 200 yards, 8 inches (2 × 4); at 300 yards, 12 inches (3 × 4), etc.
Consequently, if at 100 yards the wind were carrying your bullets 8 inches to the side, you would take two points of windage to get the bull's-eye, and if the wind were carrying your bullets 20 inches to the side, you would take 5 points of windage, irrespective of the rate at which the wind was blowing.