posted on Apr, 21 2003 @ 11:00 PM
Allow me to provide a bit of ballistic education for those enamored with the 5.56mm....
Please keep in mind that first and foremost, the .223 Remington, AKA the 5.56mm NATO was originally designed as nothing more than a varmint cartridge.
By contrast, the 7.62mm NATO was designed from the ground up as a combat cartridge, and later sporterized in the guise of the .308 Winchester round.
The 5.56mm is nothing more than a .22 bullet that gets all its magic from its hypervelocity. Take that velocity away, and you are back to square one,
a very small .22 bullet.
The 5.56mm NATO is rated for a 55 gr FMJ bullet with a muzzle velocity of approximately 3000 feet per second, generating 1099 foot pounds of energy at
the muzzle. At 600 meters, this same bullet is traveling at 1240 feet per second, generating 188 foot pounds of energy. By comparison, that is the
equivalent of a .38 Spl revolver with 158 gr bullet producing 190 foot pounds of energy at 100 meters, or a .22 long rifle bullet producing 156 foot
pounds of energy at 25 meters. At 600 meters, this bullet drops over 128 inches. (not very impressive)
The 7.62mm NATO driving a 147 gr FMJ bullet with a muzzle velocity of 2800 feet per second (a bullet almost 3x the 5.56 weight and 2/3 the velocity)
generating 2611 foot pounds of energy (2.6 times the 5.56mm) at the muzzle. At 600 meters, the 7.62MM is still traveling at 1558 feet per second,
generating 809 foot pounds of energy. This is equivalent to a .44 magnum with 240 gr bullet producing 843 foot pounds of energy at 50 meters, or 50%
more energy than a .357 magnum with 158 gr bullet produces at the muzzle, or 2.5X the energy that a 9mm produces at the muzzle. (and this is from over
600 meters!)
*All muzzle velocities are average, with standard bullet weights. Data from Sierra Reloading Manual, 2nd edition (yeah, I know its old, but the data
is still perfectly valid).
Now, as I mentioned before, the 5.56mm magic comes from its ultra muzzle velocity, but as we see above, that velocity disappears very quickly. This
muzzle velocity is also derived from the standard length 20 inch barrel of the M-16/AR-15 family.
However, the new rage in US firearms, especially in the new M4 carbine, is the much shorter 16 and sometimes 14 inch barrels. Some "entry" models
have barrels as short as 7 inches! Ever wonder what that does to the muzzle velocity, when you take that much barrel away?
From a recent gun test of a popular civilian legal AR-15 clone with a 16 inch carbine barrel, the highest recorded muzzle velocity with a standard 55
gr bullet was only 2770 feet per second, which would generate only 890 foot pounds of energy (just over what a .44 magnum does at 50 meters). Pretty
powerful for a handgun, but pretty piss poor for a rifle. Ballistically speaking, with a barrel that short, you are NO LONGER shooting a 5.56mm, but
essentially, well, lets see (flipping pages), the calibers listed with similar ballistics would be a .22 Hornet or a .218 Bee, both of which are
varmint rounds, only marginally hotter than the .22 Winchester Rimfire Magnum (as it turns out, only about 30% hotter than a rimfire bullet).
So, with a 55 gr bullet with a muzzle velocity of 2800 feet per second from an M4, at 600 meters it is at 1141 feet per second, generating 159 foot
pounds of energy, with 153 inches of drop.
Oh you say you use the 62 gr NATO load? OK, that would produce (from an M4) 2600 feet per second at the muzzle, 945 foot pounds of energy, and at 600
meters 1059 feet per second and 157 foot pounds of energy, with 183 inches of drop.
Do you really want to trust you life to a .22 rimfire????