The tribological behavior of barrel steel paired with brass, a critical interface in artillery systems, remains underexplored despite its direct impact on barrel lifespan. This study systematically investigates the tribological behavior and underlying mechanisms of this specific pairing across a temperature spectrum (RT, 200 °C, 400 °C, and 600 °C). The two materials exhibited distinctly different wear rate trends: the barrel steel's wear rate peaked at 200 °C before declining, contrary to the typical thermal softening trend. While the brass counterpart exhibited a high wear rate at RT, which then decreased significantly at elevated temperatures. A key finding is the discovery of a nanocrystalline-structured tribolayer that forms at 600 °C. This tribolayer is characterized by a distinct stratified architecture, composed of a Cu-rich top layer, a fine-grained intermediate zone, and a coarse-grained substrate, demonstrates exceptional wear resistance. This work reveals the transition in dominant wear mechanisms from adhesive or abrasive to oxidative wear, providing novel insights into the 'copper fouling' phenomenon and a scientific basis for developing long-life barrel materials.