Measuring Barrel Friction in the 5.56mm NATO
Research rept. 5 Jan 2011-30 Jan 2012
AIR FORCE ACADEMY COLORADO SPRINGS CO
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The 5.56mm NATO cartridge is used by the United States Armed Forces and the Armed Forces of other NATO Nations. Despite its wide use, current methods for finding the barrel friction of the bullet are not accurate or consistent. This paper presents a new method for finding this barrel friction by analyzing the linear muzzle energy vs. powder charge found by test firing 5.56mm NATO round with different powder weights. When graphing the relationship between the energy vs. powder charge Alliant Blue Dot Powder of the Nosler 40 grain ballistic tip lead free, Hornady 53 grain VMAX, and the Hornady 60 grain VMAX bullets it was noticed that the relationship was near-perfectly linear. This allows for the barrel friction of these rounds to be calculated by finding the vertical intercept on the graph of the muzzle energy vs. powder charge which represents the work done by friction in foot pounds. When the work of friction is divided by barrel length in feet, the barrel friction in pounds is found with an uncertainty near 3 for the jacketed lead bullets and 6.4 for the lead free bullet design. The new method of measuring barrel friction is expected to provide a quantitative way to compare the friction or reduced friction of differing bullet designs, barrel materials, bullet coatings, and polishing methods.
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