From a predictably error-filled ABC News report on scary-looking rifles:

“The way an AR-15 round enters the body … it’s designed to tumble and create a lot of tissue damage,” he said.

This is a deathless urban legend. No, 5.56mm rounds are not “designed to tumble”: The whole point of rifling (the grooves inside a gun barrel) is to make bullets spin so that they do not wobble and tumble — think of a well-thrown football vs. a poorly thrown one — and in that way to make firearms more accurate. That was the big advance from muskets to the “Kentucky rifle.”

As any hunter knows, all bullets can behave in unpredictable ways once they hit something, but the notion of special magic “tumbling” 5.56mm bullets is pure superstition. Without going too deep into the weeds here, there are several parts to a cartridge, and the actual bullet — the projectile that comes flying out of the end of the barrel when a firearm is fired — used in most AR-style rifle ammunition is the same as the bullet that comes out of almost every other .22-caliber centerfire rifle, i.e., a .224-inch bullet.

You’ll find these in ammunition for everything from AR-style rifles to hunting rifles in .22-250 Remington and .224 Weatherby. It isn’t some special weird thing — it’s just an ordinary bullet that is a lot like every other bullet.