One would have to ask....

by Byron, Saturday, November 09, 2013, 13:19 (3975 days ago) @ mcassill

What was the 5.56mm loaded with? Almost surely M193 ball which is purposely designed to fragment rapidly. The test would have turned out different if the 5.56mm was loaded with M855 which will out penetrate even 7.62x51mm NATO ball let alone the 7.62x39mm.

US M855 5.56mm vs US M80 7.62mm armor penetration:

Q. Isn't 7.62 NATO much better for long range penetration than 5.56 anyhow? Why would I want to use 5.56 when I could send 7.62 downrange instead?

Well, yes and no. For some penetration mediums like mild steel, M855 is actually superior. Consider a recent research report:

They certainly behave in a similar way when they encounter tissue at the right velocities, but they aren't exactly the same.

The SS-109 can penetrate the 3.45mm standard NATO steel plate to 640 meters, while the 7.62mm ball can only penetrate it to 620 meters. The U. S. steel helmet penetration results are even more impressive as the SS-109 can penetrate it up to 1,300 meters, while the 7.62mm ball cannot penetrate it beyond 800 meters.

The current production 7.62×51mm NATO ball cartridge has remained unchanged since its adoption by NATO in 1953. As typified by the U. S. M80 ball and the Belgian M77 ball, this cartridge propels a 147-grain cupronickel-jacketed lead bullet at a muzzle velocity of 2,800 fps (848 mps). Total cartridge length and weight are 2.80 inches and 386 grains, respectively. Utilizing a standard 22-inch barrel with a rifling twist of one turn in twelve inches (M14 rifle), the maximum effective range of the 7.62×51mm ball cartridge is listed as 620 meters (682 yards). The U. S. M80 and the Belgian M77 ball projectiles can penetrate the standard NATO 3.45 mm (.14 inch) thick steel plate up to a range of 620 meters and can penetrate one side of the U. S. steel helmet up to a range of 800 meters (880 yards). In barrier and fortification penetration tests, the 147 grain ball projectile can consistently penetrate two test building blocks.

The new SS-109 cartridge propels a heavier 62-grain semi-armor piercing projectile at an initial velocity of 3,050 fps (924 mps). The improved projectile contains a 10-grain .182 caliber hardened steel penetrator that ensures penetration at longer ranges.

The new projectile can penetrate the standard NATO 3.45mm steel plate up to a range of 640 meters (704 yards) and one side of the U. S. steel helmet up to a range of 1,300 meters (1430 yards). In tests of barrier and fortification penetration however, the steel penetrator of the SS-109 could not pierce any of the test building blocks.