Over penetration has always been an issue thus the need for knowing what is beyond your target. A serious shooter will adjust his shot angle to ensure that a pass through has no negative consequences. This is not new doctrine.
I was paid to attend some training w/ Ayoob in his hayday during the '80s. His retention and other hands on techniques were a joke that depended on a compliant opponent for success. We trained in helmets w/ a mouthguard and cup. He did not enjoy being challenged or hurt.
mike r
Don't wish it were easier Wish you were better
Stab them in the taint, you can't put a tourniquet on that. Craig Douglas ECQC
