The US cartridge, blank, M200 is ubiquitous in Army training. Designed to give the port pressures of standard US 5.56mm ammo, it is used in training with a blank adapter to realistically replicate the sound and function of ball ammunition. It's very effective in familiarizing folks with the sound of an M16.
Recently, I got a heads-up that I may be asked to do some training in which it might be effective to show folks what common 5.56mm ammo sounds like, so I started casting about for a source of blank ammo. I was somewhat surprised that Ammo To Go stocks the stuff, so I gave them a credit card number and they promptly sent me some. It came in today.
Talk about a trip down memory lane. Now, I just have to find a blank adapter. Amazon sells them, but I think I'll look around before I make an order. If any of you old soldiers has one, I'll make you a good deal on it.