Document Type

Undergraduate Project

Date of Degree Completion

Spring 2017

Degree Name

Bachelor of Science


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.