Document Type


Date of Degree Completion

Spring 2017


Mechanical Engineering Technology

Committee Chair

Seth Rich


There is an increasing need for singular weapon systems to fill multiple roles. A fire control group system is needed which provides a trigger that is adaptable for different uses on command by way of the safety selector. The device needs to be non-intrusive to normal function and operation of the firearm requiring no specialized training in its use. It should provide with a setting for a general combat use and a secondary setting for a designated marksman role. The proposed system interfaces with existing trigger groups by using a self-contained drop in module that counteracts the primary trigger spring while set to the second fire mode. By using a secondary spring to counteract the primary spring the end result is essentially a lower k value on trigger movement reducing the trigger pull weight. A survey of commonly available triggers shows a range of trigger pull values for combat triggers to be 5-7 lbf and marksman triggers to be 3.5-5 lbf. From this data it is concluded that the module should provide a 1.5 lbf reduction in trigger pull force when engaged in the second fire position. This provides a singular fire control group system that has the ability to serve in both a general combat and designated marksman role. The characteristics of the entire system may still be tailored to personal preference by the selection of the trigger group the device interfaces with.