Inaccuracy in Sight Scale Markings

By J. R. Mattern

American Rifleman, vol 62, No. 20, Aug 11, 1917 – pages 385, 390

MYSTERIOUS groupings and misses with many Springfield and Krag rifles often can be traced to irregularity in the range scale markings stamped on the leaf of the rear sight. Many owners of these rifles think that the scale is to be accepted as gospel, but that this cannot be done with all rifles is illustrated by the findings of a recent test of half a dozen military rifles with a precise sight gauge.

The gauge tells a surprising story and one that was not even suspected by the men who shot the rifles. On the rifle with the most striking inaccuracy of sight marking, which will be used as an illustration, between the 100 yard mark and the 200 yard mark the gauge registers 2 degrees of elevation. Between the 200 yard mark and the 300, it shows that there are 4 ½ degrees of elevation. In this there is nothing to be alarmed about greatly, though the increase from 2 to 4 ½ degrees seemed somewhat out of the proportion.

Between the 300 and 400 yard marks, however, the difference of elevation is only 2 ½ degrees, which is practically the same as between 100 and 200 yards, and only half as much as between the hundred yard marks preceding! This obviously is an error great enough to cause serious trouble on the range, but which can not be detected on the sight leaf by ordinary observation. Between the 400 and the 500 yard marks there is a difference of elevation of 4 degrees, which is more like it ought to be, and yet not enough in comparison to previous elevations, since it is well known that the bullet falls at a faster or greater rate over each succeeding hundred yards of flight.

The irregularities of elevation for each hundred yards between 500 and 800 are not quite so striking as below the 500 yard mark, but still are enough to cause trouble on the range. Above the 800 mark, a uniformity that is refreshing shows itself. The details are given in the attached table, and need not be commented on here other than to point out that the ratio of increase for each hundred yards is even. If this even ratio is correct at this part of the scale, it should be correct for the lower part.

The table tells the rest, better than anything else can do:

(Note—Fourth column totals up 1 ½ degrees less than the actual increase in degrees between 100 and 1500 on the sight scale—see third column. Hence the fourth column is accurate only to within one-eighth degree at the points marked with -.)

On this rifle the 200, 300, 400, 500 and 600 yard marks are out of place 50 yards or more. Other range marks are out, too, but only 10 to 20 yards, which do not make such great difference, especially as the marks all are uniformly lower than they should be. The 400 yard mark is a full 100 yards out of place, and the 500 yard mark 75 yards wrong. The outstanding feature developed by the test is that the owner can not set the sight according to the scale, or according to any fixed relation to the scale, as for instance, a certain number of yards or degrees of sixty fourths of an inch higher than the corresponding range in any case, as is the custom. If he does he gets badly fooled when he fires. The only thing he can do is to target the rifle at each range, and record and memorize the irregular elevations required to land in the bull. Even at that he is at a serious disadvantage when it comes to changing the sights for varying ammunition, or to shooting in another position than the one used in arriving at the recorded figures.

The fourth, fifth and sixth columns in the table are designed to give data that illustrates both the correct position for the marks on the sight leaf, and a working basis for shooting this and other rifles carrying such irregular markings. The figures in the fourth column are entirely arbitrary—that is, they are not the result of computation in connection with known trajectory and other figures for the Springfield rifle and cartridge, but are set down to show more plainly by comparison with those of the third column the errors under discussion, and to present concretely the definite and consistent relation that the marks on the Springfield sight leaf ought to bear one to another. The figures in the two last columns may or may not be correct shooting elevations at the ranges specified, but if one figure is high or low they all likely will be wrong to the same extent exactly, which makes correction easy and regular throughout the series by the simple addition or subtraction of the required number of degrees. The marks on the sight leaf of the rifle should be just as regular, and just as easily used as a basis for correct adjustment at any range

The sight gauge is a particularly desirable little tool for the man with an inaccurately marked sight leaf. It enables him to begin his calculations with the lowest or 100 yard mark on his sight leaf, and to make corrections for different ranges, varying ammunition, light, moisture, temperature, positions and other factors positively and accurately. It also serves as a check against marks wrongly placed.

Many rifles are marked correctly, as a test will demonstrate. The writer had one on which every mark seemed to be just right. But enough of them are marked wrongly to justify every owner in checking up. This applies to Krags as well as Springfields. After the test each man can work up a table for his own rifle such as the one attached, and can paste it on the back or front of his score book for quick reference. To be thoroughly familiar with the uniform elevations for each range is particularly of advantage in certain parts of the N. R. A. qualification courses that require quick setting of sights.

It is unfortunate that the sight leafs are not all marked correctly, but incorrect marking need not interfere with accurate shooting and the making of high scores if the owner of the rifle becomes aware of the conditions and arrives at a proper basis for making his adjustment at each range. The gauge is the easiest means of meeting the problem, though other means of measuring, or even careful targeting, may be made to serve the purpose.