A friend of mine is a retired cop/detective.
He tells stories about all the stuff he has seen 9mm bounce off of.
I think ems and emergency room folks have seen the same thing.
the gel is supposed to be the average of the human body density. They are trying to be scientific and have repeatable tests etc. The problem is that the human torso is not uniform density, it is surrounded by a ribcage which can deflect bullets, esp lighter and low velocity bullets.