Influences of Rifle Weight, Weight Distribution and Layout on Aiming Comfort

A rifle in a soldier's system is often equipped with a grenade launcher, aiming device, etc., which increases the weight of the rifle and changes its center of gravity. This study explores how the rifle weight, weight distribution and layout (e.g. stock length, position of grip and forestock) affect aiming comfort. In the paper, the upper extremity muscle activity was used to characterize the aiming comfort. A human-rifle musculoskeletal model was developed, which was validated by the surface electromyography (EMG) data. The results showed that the design parameters of rifle (weight, distance of gravity center to body and layout) had a significant influence on aiming comfort. The greater the weight was, the stronger the muscle activity was. With the distance increasing, first the muscle activity decreased, and then increased when the distance is exceeding a certain value. In addition, the combined influences of weight and distance illustrated that there was an optimal distance to make the slightest muscle movements for certain weight. For designing a rifle's layout, more muscular exertions were required to maintain the holding posture with the stock length increasing, which was suggested to be in the range of 0.18.m to 0.27.m. Results can be used to optimize the ergonomics design of rifle, improving the comfort of the rifle aiming process and the shooting accuracy.