A .32 acp in the boiler room will take em down just fine. All day long. A .38 or 9mm will do it magnificently.
And with a money back guarantee for almost instantly if its a contact shot. Their “toughness” is simply a part of the trite persona and culture of people who love to imagine how tough their dogs are, and by extension, them too.
While I think you are right on caliber selection, the real issue is hitting the dog with any shot while it is biting your shooting hand and breaking all the bones in that forearm.
The only way I see to accomplish this is to shoot the dog before it gets close enough. This is way outside the 7 yard range for a man with a knife, maybe 10 yards.
Who is going to back me up legally if I shoot a dog who growls at me from 30 feet away?