Fact is, it's not. The specific ammo of 5.56x45 nature this rifle was designed to use is a .223(4, for purists) varmint round but with full metal jacket as required by the Geneva Convention. It is designed to puncture but not necessarily kill. In the mid-1970s, a 5.56 ammo manf designed the SS-109 wasp waist, which was later changed into what is now the M855 light armor piercing round. This round uses a 62 gr bullet as opposed to a 55 gr, and is less stable in a 1-8 twist machine. This causes the bullet to destabilize in soft targets more quickly, but retains stability through light but resistant materials. In either case, the AR-15/M-16 and variants have a longer and narrower wound channel than the M60/M240 7.62x51 (308 Winchester). Some will argue that the 308 is a much heavier and more potent round, and will therefore penetrate more of that flesh, but that simply is not true, based on ballistic gel testing. So if you want to pulverize/shred flesh, use an AR-10 or hunting rifle in 308 Win. Incidentally, the Serbian NATO 7.62x51 145 gr FMJ has better penetration through hard material, but still has exceptionally good shocking power, so will blow the brains right through that blue helmet. PPU is a good source if you can get it.