Effective Kill Shots?

My HOA recently hired me to take care of the pest problems around the neighborhood. I decided to buy a pellet gun instead of risking it with a .22 long. The pellet gun produces around 6 ft-lbs of energy at the muzzle and I know that this is an effective kill against rats and sparrows if shot in the head. My question is, will this be an effective kill with a heart/lung shot? This will increase the percentage of pests I am able to take.