On the Probability of Penetration of Armor Plate
OFFICE OF SCIENTIFIC RESEARCH AND DEVELOPMENT WASHINGTON DC NATIONAL DEFENSE RESEARCH COMMITTEE
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The probability of penetration for projectiles with measured velocities near the ballistic limit has been experimentally determined for caliber .30 A.P. Mark II bullets fired against a particular plate of 12-inch homogenous armor of Brinell hardness 415 manufactured by Disston. Various ways of treating the data have little effect on either the ballistic limit or the standard deviation, which have values in the range 2315-2322 ftsec and 2327 ftsec, respectively. In particular, corrections for variations in bullet weight are found unimportant. It is shown that if the standard deviation for firings of this particular caliber, bullet type, method of measuring velocity, type of plate, and so forth, is known, the ballistic limit of a similar plate for similar conditions can be determined with good accuracy by two bracketing shots. Specifically, if the standard deviation is 25 ftsec and two shots are fired that differ in velocity by 25 ftsec, the higher velocity shot penetrating and the lower velocity shot failing to penetrate, the ballistic limit may be takes as half way between the two velocities with a probably error of 17 ftsec. If the bracketing velocities differ by 50 ftsec, the probable error is 19.5 ftsec.
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