Cool story, broThere's a big difference between firing without earpro in a non-stress situation and firing in a stressful situation. Don't encourage unnecessary hearing damage to acclimate somebody to something they won't even notice in a time of high adrenaline.
I've had to fire indoors before and didn't notice anything but muzzle flash (I recommend a good flash hider) and ringing ears later (which I already have in the form of wonderful tinnitus).