Is this video of a solider getting his cap shot ioff real or not?

Seems real but these days who can tell.

Is this for real? Do they really use live ammo in these salute exercises?

No, it’s a blank. The evidence of that is that the soldiers have to charge the weapon after every shot because a blank does not cycle the action on an automatic weapon.

A blank has more than enough explosive force to do that at close range, though. There have been a number of people killed by blanks at close range because they had no idea that blanks could be deadly. There is still a considerable amount of material that comes out of the barrel at high speeds.

I seem to recall Mythbusters showed it was pretty much impossible to knock someone’s hat off with a bullet.

From a distance, it is about impossible to knock a hat off with a bullet, unless it’s a really hard hat. Otherwise the bullet will just go right through it. If you are close enough, though, either a bullet or a blank will knock a hat off, though in either case it is really the expanding gases from the gun barrel that are knocking the hat off.

If they had been using real bullets instead of blanks, the unlucky soldier in that video would have still probably had his hat knocked off, but only because the guy who accidentally fired was so close behind him.

Also, as Airman Doors said, blanks can kill. Even though they were using blanks, the unlucky soldier who got his hat blown off could have been killed if the guy behind him had been aiming a bit lower. Actor Jon-Erik Hexum was killed by a blank in the 80s.