AR Manufacture and Cartridge History

The AR started out as being designed for the military market by ArmaLite who ran into financial problems and sold the designed to Colt who redesigned the gun a little more and the gun was adopted by the military in 1963 The gun was originally not well liked by the soldiers in the military as it had functioning problems and the cartridge needed a different powder charge. Some were told to shower with the gun and one of the interesting instructions was to strike the gun butt on the ground and if jams persists turn in for repair. This is not even fine for a civilian market but for the military this must have sent dread and fear to the heart of a soldier. Some have said that if the opportunity arose they would have dropped their gun in favor of picking up an enemy AK 47. 

The cartridge was a scaled down 30/06. The 30/06 was a very efficient cartage and got its name 30 caliber #6 attempt in the development process or 30/06 for short. The scaled down cartridge was to use a 22 bullet whose goal was to injure the enemy and leave the enemy to care for them. This is an example of where our western idea of fairness was mistakenly placed on a foreign battlefield; This did not work in Vietnam as if the enemy was not able to walk he was shot by his own people. Knowing that they were dead anyway when our soldiers walked passed them they would shoot a US soldier. This started the practice or we should call it a necessity to shoot the downed man a second time before you walked by him. The Arab terrorists work the same way so our soldiers must shoot them a second time before they can go near them. Back in the day this was called double tapping but today to be politically correct it is called controlled seconds.
  The cartridge was called 223 Remington cartridge later would be adopted by NATO with a heavier powder charge and grater muzzle velocity as 5.56X45 or 5.56 for short. Whatever the cartridges deficiency it has the distinct advantage of letting the guns user carry a lot of ammo compared to 30/06 or 308 or even 7.62X39. At fairly close range the bullet caries a vacuum behind it which on impact creates about  3000 psi in the torso  and it would pay you to watch  a ballistic gelatin video on the Internet in slow motion. The cavity is expanded and the damage is not just from the hole the bullet makes but by the inflation rips and tares creating massive internal damage. The bullet many times bounce around in the body surrounding tissue from bone to bone. So whether fired from close or longer ranges the bullet will ricochets around the body creating more damage along with the vacuum effect.
Richard W. Norman Author of American Handbook on Guns Ammo and Freedom