Charlie Sheen's in for some bloody disappointment if he actually wanted to blow a guy's head off with a Super 90 shotgun -- because the gun company tells TMZ, the worst damage their gun can do is "leave a really big hole."
A rep for Benelli USA -- which manufactures the famed Super 90 shotgun -- tells TMZ, the semi-automatic shotgun might also just "make a lot of smaller holes," depending on the distance.
But one thing's for sure, the rep tells us, laughing, "It's impossible for him to blow someone's head clean off."
TMZ broke the story ... Charlie's been accused in a police report of threatening to off a former associate with a Super 90, texting a mutual friend, "I'll blow his head off." Cops want to talk to Charlie about the situation asap.
FYI -- the Super 90 comes in 3 different varieties ... the M1, M3, and the M4 (military grade) ... so Charlie's got a few different choices.