Hello! And welcome to the forum! I'm just going to tell you the honest truth here. If you do not have legit registration papers to see the bloodlines, there is no way to tell what type of bully breed dog you have. You have a mutt which means "dog of mixed or unknown orgin."
Just going by looks doesn't work with bully breeds as there are so many breeds that all resemble each other. However, I will say that your dog looks nothing like an American Pit bull Terrier, an AmStaff, or an American Bully. He looks like an American Bulldog mix to me.
But unfortunately, you will never know his breed as you don't have legit registration papers to look at bloodlines.
When people ask what you have, just be honest and say you don't know what breed he is, just a big bully breed type dog!
Having a mutt doesn't make him any less of a dog! Almost all the members on this forum have at least one or have had one!
hope you stick around!