Rewrite History!
You go back to prehistoric times, point your .45 at the first human, and pull the trigger.
This causes a major rip in the space-time continuum and YOU HAVE JUST DESTROYED THE WHOLE UNIVERSE AND EVERYTHING THAT HAS EVER EXISTED By killing the first human, whom you are a descendant of, you caused a paradox which time could not understand. This caused a massive electrical storm, which has destroyed everything that ever existed in any time whatsoever.
NICE JOB, MORON!
This causes a major rip in the space-time continuum and YOU HAVE JUST DESTROYED THE WHOLE UNIVERSE AND EVERYTHING THAT HAS EVER EXISTED By killing the first human, whom you are a descendant of, you caused a paradox which time could not understand. This caused a massive electrical storm, which has destroyed everything that ever existed in any time whatsoever.
NICE JOB, MORON!