An adjustable fire control for firearms having as series of adjustable engagement settings between the sear and the trigger, including a trigger engagement adjustment including a preset engagement and an adjustable engagement for setting the amount of displacement of the trigger with the sear for firing the firearm. In doing this, the pressure of the refrigerant in the low pressure portion of the circuit, including the evaporator, and the mass flow rate of the refrigerant remain substantially constant. These compounds may be used as additives andor removed from soy-based foods, beverages, cosmetics and medicinals in order to modify T2R-associated bitter taste elicited by bitter ligands present in hydrolyzed soy protein materials. An upper encloses the heel and forms a pocket for receiving the head of a golf club.