Also the German Shepherd has about 100# +/- stronger bit then the pit bull. The Pit Bull can lock and hold his bit longer.
Sorry to be "that guy", but this is completely untrue and is how myths get propagated, by passing on untrue or exaggerated information. I have over a decade of experience working with Police K-9's, personal protection dogs, guard dogs, prison dogs, DEA, US Customs, tracking dogs etc. I have also bred some working line German Shepherds for serious personal protection, and competed in both Schutzhund and French Ring Sport with my own dogs. I worked with over 10 different local law enforcement agencies when I lived back east. Lets just say I have plenty of experience working with dogs trained to do damage to humans. Yes, I went to school for this! Anywho, I feel reasonably qualified to step into this convo and interject a few cold facts.
The German Shepherd Dog (GSD) is pretty much the world-wide standard for almost every type of law enforcement work you could think of. Lately though, the Belgian Malinois breed are becoming popular in this type of work too, but I digress. The GSD is exceedingly intelligent and easily trainable, and puts out just enough bite force to grab and hold a suspect, without causing too much tissue damage on the combatant. There is a VERY GOOD REASON why Pit Bulls are not used in this line of work, as their bite force is ridiculously high compared to a GSD. Rottweilers also put down too much bite force to be used for serious Police work. Their bite would be too much of a legal liability for the department, as it would fall under Police brutality and/or cruel and unusual punishment scenarios. I personally witnessed a Rottweiler owned by US Customs, break both a suspect's forearm bones in an apprehension, and the dog was immediately retired after that.
Most of the "bully breeds" have a large broad skull framed and topped by enormous, exaggerated muscles that contribute to the clamping force their jaws are capable of. Notice the GSD's skull is much more narrow and framed by much smaller jaw muscles, indicative of the amount of force they are capable of. No dog can truly "lock" its jaws, this is a myth. They simply bite and hold on. A well trained police quality K9 GSD will immediately release its jaws when given the command by its handler. This reaction is bred for and encouraged. A dog that will not reliably let go when told to do so, is a liability for the police department and would never be used on the street, nor would it graduate the K9 Police academy.
There is a device called a dynamometer, that we used to measure the bite force of the dogs we trained. As I remember it, a GSD was around 540 lbs of force. A pit bull can easily put FIVE TIMES as much clamping force in its jaws! I have seen 3200 lbs of force register on the dyno, from a Bandog, which is a hybrid of Neapolitan Mastiff and Pit Bull Terrier. That much clamping force is impossible to dislodge, which is what (erroneously) led people to believe that certain dog breeds can lock their jaws.
When a dog clamps its jaws down on something it was chasing, where their "prey drive" has kicked in, at the moment they catch their quarry, their body releases endorphins into their bloodstream. This is their "reward" for the hard work of chasing and apprehending their prey. Once a pit bull has clamped down, good luck trying to get them to let go of whatever it is they are biting! There are special tools called "Break Sticks" that are known to pit bull people for the unsavory job of prying the dogs jaws apart once they've set their teeth into something. I am in no way disparaging the pit bull breed, I am simply stating well known facts. Also, Pit Bulls were bred for hundreds of years for dog aggression, so it became instinctual behavior for them. It is very difficult to know ahead of time, what may set the dog off. They are cool dogs, dont get me wrong, but they are still an animal that is not 100% predictable.
BTW, I currently own two Bully breeds. I could tell you some stories.....