Effects of Temperature Changes on the Mechanical and Ballistic Responses in Biathlon Shooting

Background: Biathlon is a nordic sport that combines cross-country skiing with rifle marksmanship. It was reported that standing shooting was significantly affected because skiing exercise usually decreased the postural control of biathletes and increased the shooting time. Another hypothesis that may explain the decrease of one’s shooting accuracy after a cession of cross-country skiing could be linked with mechanical factors. The goal of the present study was to examine the influence of negative temperatures on the trigger mechanism and on the ballistic responses of the bullet. Method of approach: In order to determine the possible variations of the force required for triggering, five biathlon rifles were equipped with strain gauges fixed on the trigger. A thermostat vessel was used to control the temperature changes at room temperature $(+20°C)$$(+68°F)$ until $−20°C$$(−4°F)$⁠. Concerning the ballistic measurements, eight series of five shots were performed at $+20°C$$(+68°F)$⁠, at $−3°C$$(+26.6°F)$⁠, at $−10°C$$(+14°F)$⁠, and at $−20°C$$(−4°F)$⁠. The shooting precision was assessed by determining the group diameter (GD) and the shooting score (Sc). Results: The results showed that from $+20°C$$(+68°F)$ until $−8°C$$(+17.6°F)$⁠, the triggering force was equal to $5N$$(1.12lb)$⁠, whereas at $−20°C$$(−4°F)$⁠, a triggering force of $8N$$(1.8lb)$ was required. The increase of the triggering force that was found under $−8°C$$(+17.6°F)$ could be caused by the difference between the coefficients of expansion of the different materials constituting the trigger mechanism. Concerning the ballistic measurements, GD at room temperature was significantly lower $(P<0.05)$ than $−3°C$$(+26.6°F)$⁠, $−10°C$$(+14°F)$⁠, and $−20°C$$(−4°F)$⁠. Furthermore, Sc was significantly better at $+20°C$$(+68°F)$$(P<0.05)$ compared to $−3°C$$(+26.6°F)$⁠, $−10°C$$(+14°F)$⁠, and $−20°C$$(−4°F)$ conditions. Conclusion: It can be supposed that the degradation of GD and Sc could be due to the formation of frost in the barrel and by the difference of the expansion coefficient of the bullet-barrel materials. Consequently, both mechanical responses could partly explain the shooting accuracy impairment observed in negative temperature shooting conditions.