Major, Ordnance Department Reserve The Army of the United States
Sketch* by LT. COJL JULIAN S. HATCHER
Small'Arms Technical Publishing Company Onslow County, North Carolina U. S. A.
Thomas G. Sam v/orth September, 1937
All right* reserved ppit*«
The frontispiece illustrates a characteristic velocity and pressure curve plotted far different charges a3 explained on put« 12S and 130. This Is a typical curve and does not represent figures published anywhere "or for any definite rifle, cartridge or bullet. It Is seen that the velocity curve Is virtually a straight line, thus showing that as the powder charge Is increased the velocity is raised in a proportional amount. This means, therefore, that within the limits of the powder charges published. It is entirely feasible to estimate the velocity of any other powder charge by direct proportions as explained on page 12$.
It is seen also that the pressure increase is not a straight line, nor Is it in direct proportion to the powder charge used. The amount of curvature of the pressure line depends largely on the characteristics of the cartridge and the particular powder used. The quicker burning powders intended primarily for reduced loads or mid-range work will show a sharper pressure rise for a given charge increase than will the larger grain, slower burning powders. Consequently, for such faster burning powders, the maximum pressure level, safe to use. is lower than normal for the full load of slower burning powders usually for maximum loads. At low pressure levels, i. e., when using reduced charges, practically all powders will show relatively small pressure Increases in proportion to the increase in charge. However, at or near the maximum charges published for a given powder In any cartridge, the pressure Increases at a very rapid rate and •ufc of all proportion to a unit increase in powder charges as illustrated by the sharp upward turn of the curve at its upper end. This characteristic pressure curve illustrates that between the charges published for any powder, It Is perfectly safe to interpellate or calculate the pressure developed for any intermediate charge by direct proportion which would, of course, be the same as if the pressure values were read off the dotted straight line connecting two adjacent plotted points. This curve also illustrates that It Is dangerous to attempt to estimate the pressures developed by extrapolation or extending the pressure curve beyond the maximum charges published for use with a powder. A few grains more powder, or under some circumstances, even a slight increase over the maxim am charge may develop Infinite pressure.
The published powder charges and ballistics obtained represent actual tests made with present day components. Many re-loaders seem to go on the theory that the powder charges published are actually cut or lowered a grain or two for the ballistics shown and, therefore, they will play smart and deliberately increase the charge to offset this modesty on the manufacturer's part. Fot intermediate or low pressure loads it is seen that this can do no harm In the way of developing dangerous pressures, BUT for full charges or maximum powder charges published, such a mistaken idea may very well re*ult in excessive pressures with resulting damage to the gun and possible injury to the shooter.
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