ya.. amstaffs tend to be a lil heavier than game bred pitbulls! as guard dogs, when trained, they guard.. they are not as good as GSDs in guarding.. but when they feel the need to protect n start protecting, you know what they are capable of.. this video itself speaks about it!
an amstaff labelled as pitbull was eager to meet me! that person owned 3 of such dogs! he said that they are friendly to humans, but a terror to other animals! 2 males won't get along and 2 females don't always get along! but a pair does fine..