Isn't that a Feng Shei accupressure/ Rolfing deep massage nub? It helps recenter your chakras, after they get put out of whack by the muzzle blast. Be sure to shoot tracers, the red light they make is very harmonius and uplifting, and will leave a smile on your face that only the enlightened truly know.
Remember Confucius say, "Tracers work both ways."