Just tell him not to do the reverse experiment. My own personal rule is only one box of shells on the table at any given time. And I have big, bold writing on all ammo containers.
I haven't fired anything in the wrong gun, but last time I made it to the range, I took my .204 rifle, and .17 Remington ammo. Whoops. And of course, the .17 box is the only one that is not marked as to what it is. That reminds me. Gotta go mark that box.
