Back in the day of black powder, bullets where cast solid from lead or a lead alloy. Antinomy has the property when added to lead to harden the bullet to prevent deformation prior to shooting. Antinomy and lead is leading alloy for bullets and have been for some time. Bullets may have been wrapped in paper at the base and were called ‘paper patch’ bullets. This protected the base of the bullet from the direct contact with the hot burning combustion products of the propellant and thus decreased the fouling from lead coating the bore.
Full Metal Jackets
When smokeless powders hit the market velocities were high enough to cause leading of the bore and necessitated the metal jackets of copper or brass. Remember that brass is a copper alloy with zinc. Brass is a good material with high resistance to corrosion and used for the cartridge case but as copper is a strategic material having applications in many industries, the price of the copper can make brass costly. Later in the 20th century many European countries shifted to lacquer coated mild steel for cases and jacketing. The jacketed bullet does not allow lead to contact the bore and reduces fouling. With the prohibition of deformation of bullets in combat between uniformed members of the conflicting armies whose countries were signatory to the Hague Convention (US never signed) a method to control expansion was needed. The full metal jacket is jacketed from the point to the base with lead exposure on the base. Bullets are formed by placing a lead slug inside a drawn jacket then crimped at the base. Military bullets are formed point first with an exposed base. Sporting numbers are formed base first with an open expanding point.
Best Sniper Bullet
The bullets used in sniper rounds are currently the Hornady 175 grain hollow point. The point is crimped tight and the heavy jacketing prevents expansion. But there are other methods to increase the lethality of the bullet. The British .303 and current Russian WWII rounds are designed to tumble when hitting a denser medium, like the human body. Most bullets are designed to be stable, but marginal stability in the air with the center of gravity moved towards the rear will cause the bullet to upset and tumble end over end, all without expansion in tissue and minimal deformation when hitting bone. Most modern military rounds will tumble.
Non Lead Bullets
A fully encapsulated bullet has a base plate with the jacket crimped to fully seal the lead core from the environment. With the court mandate that the military do away with leaded projectiles, there has been considerable effort surrounding the development of the new M855A1 non-lead ‘green’ bullet. With an exposed steel penetrator in a copper jacket and a 1:9 twist rate (current is 1:7) 95% of the rounds will hit within an 8-inch circle at 600 meters. The jacket is crimped to a cannular cut in the steel penetrator. In the older 1:7 rifles the groups open up and are less accurate.
Ice picking is the term used to describe through and through bullet travel without causing significant trauma when using the current M855 bullet because of its low yaw and highly stabilized projectile due to the 1:7 twist. Yaw is what controls the tumbling in tissue. It is a factor of velocity, density of tissue, angle of impact and point of impact. In Afghanistan many of the insurgents are malnourished with torso of only and average of 7.5 inches with the M855 needs 7 inches of penetration before the bullets stabilization and yaw is overcome allowing tumbling. The M855A1 is designed to yaw at 3 inches of penetration beyond impact. The new round will punch through 3/8” steel plate at 350 yards when fired from the 14” barrel of an M4. This significant because in Afghanistan there were reports that the older M855 round failed to penetrate the steel doors of cars.
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