Would my dog be an American Bullmastiff papers says Aussie Mix chip mastiff mix ex-owners said he is Australian Shepherd with boxer in him could a bullmastiff resemble pit?

Based on the information you have provided, it is possible that your dog could be an American Bullmastiff, although it is also possible that it is another mix of breeds.

The American Bullmastiff is a relatively new breed, developed in the United States in the 1930s by crossing the English Bullmastiff with the American Pit Bull Terrier. They are typically larger than the English Bullmastiff, with males standing 25-28 inches tall at the shoulder and weighing 100-130 pounds, while females stand 23-26 inches tall and weigh 80-100 pounds.

The American Bullmastiff has a short, dense coat that can be any color, although brindle is most common. They have a broad, massive head with a short muzzle and strong jaws. Their eyes are typically dark brown or black, and their ears are small and set high on the head.

The American Bullmastiff is a friendly, loyal dog that makes an excellent family pet. They are intelligent and trainable, but they can also be stubborn. They are typically good with children and other dogs, but they can be wary of strangers.

If you are concerned about your dog's breed, you can take him to a veterinarian or animal shelter for a DNA test. This will tell you for sure what breeds your dog is mixed with.