Friction Effects of Lead-Based and Lead-Free Primers in 5.56mm NATO.

摘要

A possible dependence of barrel friction on primer type was discovered in a previous project. The purpose of the present study is to quantify friction effects of three different small rifle primers (one based on lead styphnate and two based on diazodinitrophenol, DDNP). When powder is carefully selected to have a near perfect linear response between muzzle energy and powder charge, the resulting vertical intercept of a best-fit line represents the mechanical work done pushing the bullet through the rifle bore or the energy lost to barrel friction. Thus the average frictional force is simply the energy lost to barrel friction divided by the barrel length. This method determined the energy lost to friction to be 376 ft lbs (+/- 35 ft lbs) when using the Russian made (Murom) DDNP based primer and a 62 grain jacketed lead match grade bullet (Berger Flat Base), which was significantly greater than the 330 ft lbs (+/- 2 ft lbs) lost to friction using a lead-based primer (Fed 205m primer, made by ATK) with the same bullet. The American made DDNP based primer (ATK) produced a measured 322 ft lbs (+/ - 40 ft lbs) lost to friction. The large uncertainty in the friction determination with the ATK lead- free primer was caused by velocity variations and made its friction statistically indistinguishable from either the Murom lead-free primer or the Fed 205m lead-based primer. A table in the appendix summarizes bullet friction measurements to date for 13 different bullets under a variety of experimental conditions (twist rates, primer, bullet coating, etc.). Bullet friction measurements are included for the M193 and M855 bullets with and without the petroleum based sealant added between the bullet and cartridge case.