If you fire too many rounds down a real gun in quick succession at best you will destroy the barrel at worst they will be picking bits of receiver out of you.
Not correct, just watch a few YT videos of competition shooters in the US hosing down stages with no issues, then look up a 'melt down' video to see the crazy volume of non-stop automatic fire it takes to actually break something on even a commercial firearm that's not designed or built to be used in automatic. The info/evidence is widely available.