My older brother and I would play in the backyard with plastic army men, setting up battle lines about ten feet apart with dirt embankments and plastic soldiers strategically placed along the dirt embankment. My brother and I would stand off to the side of our mock battlefield and simultaneously start shooting the other guy's soldiers. The winner of the battle was declared when the last guy's soldier was taken out.
I confess my brother and I would also get in direct BB gun fights with each other which resulted in some pretty good welts on our bodies, but no significant injuries.
Fortunately, as a result of these experiences, neither of us grew up to treat real guns as play guns. We both appreciated the difference between BB guns and real guns.