What do you think? I've got a dummy .50 cal round, and it looks pretty good as a gouger or a pressure-pointer. I think a couple jabs to the soft parts of the lower neck/upper shoulder, or rips, or even face if need be would deter someone.
However, if you're that close, you've made a mistake anyway, right? But this is not a strategic thing, really just thinking about that round as an improv weapon.
Maybe a 20mm would be better?