One of the largely unreported changes in infantry rifles over the last two decades has been the switch to armor piercing bullets. While the AK-47, and early M-16s, used a lighter bullet that tended to tumble when it hit something (and cause a more massive and debilitating wound), NATO nations took a different approach when they began to adopt the M-16 type rifle in the 1970s and 80s. The early M-16 bullet weighed 55 grains, while the current one is 62 grains (13 percent heavier). Moreover, since the introduction of the SAW (Squad Automatic Weapon, a machine-gun version of the M-16), the rifling was tightened to give the bullets more spin, mainly so that the tracer rounds the SAW used (so the gunner could see where all those bullets were going at long range) followed a more stable flight path. The NATO standard SS109 round (which the U.S. has to use, being a member of NATO), has greater armor piercing capability, but wears out the gun barrel more quickly and causes less disabling wounds (for example, an SS109 bullet hitting a leg would tend to just go right through, while the lighter, older bullets would tear up the leg without passing on.) The SS109 is also six percent faster (at 3280 feet per second) than the M193 round (except in the shorter barrel M4, where the SS109 travels at 3049 feet per second). The SS109 has not seen enough combat to allow one to say whether it is a more, or less, capable bullet than the older U.S. M193. But someday, there will be enough evidence. For fighting against unarmored opponents in a place like Afghanistan, the older M193 bullet would probably be more effective. But against a foe wearing steel helmets and body armor, the SS109 would be more effective. It's quite possible that, in any kind of combat, there is not appreciable difference between the two types of bullet.