We did an interesting exercise once with airsoft guns. The shooter stood in the middle of 4 BGs. You closed your eyes and had to open them to find your opponent and shoot him as fast as you could. Not realistic but fun.
We found that all of us had airsoft hits around the belly button, and they stung. I once got hosed at close range with a full auto airsoft gun and it broke the skin (quite a few times) through a t-shirt.
The belly button hits demonstrated that even with practiced shooters, we fired before we had the sights on COM or mashed the trigger under time and stress. Fun to see big strong guys go Ouch during navel warfare.