Several prominent self-defense trainers, like Larry Vickers and Rob Pincus, now advocate or acquiesce to the use of 9mm as a defense round. On the other hand there seems to be a consensus by them and others that a "trail gun" or "backpacking gun" -- something you take into a place where a medium to large animal might attack -- needs to be 10mm or larger. It seems to have something to do with bullet diameter, bullet mass and velocity. If those are the primaries when you are facing claws and teeth, how come they are not the primaries in urban self-defense? Wanna kill these ads? We can help!