Oh, I've got an even better one than that ...
Guy in my training CO spent 5mins (which is an eternity when you've got half a company ready to go) on the firing line at the qualification range trying to get his M-16 to feed correctly, got all the Drill SGTs over there watching him and everything .... turns out, he had put the magazine into the well
upside down. Yes, it is possible to jam the bottom end of a 30-rd GI mag into the well of an M-16, if you slam it hard enough. SGTs had a hell of a time getting it out of there, too.
He took crap for that for the rest of Basic. Probably ended up in the Chemical Corps (with apologies to anyone from Chemical).
As to the armor penetration of the AT4, very few modern armored vehicles have rolled homogenous armor plate. It's just used as a metric for comparing different armor systems. There are probably composite ceramic/alloy materials that can equal 16" of homogenous steel and still only be 2-3" thick. (Google 'Cobham Armor' if you want to learn more.)