Addressing the characteristics of high reliability and limited failure data in firearms, this study aims to account for uncertainties in the firearm failure process and employ the initial projectile velocity as an indicator of barrel degradation to predict the remaining barrel lifespan. We establish a degradation model for the initial projectile velocity based on a nonlinear Wiener process and create a gun barrel residual lifespan prediction model that takes into consideration the randomness of the life threshold. We employ the maximum likelihood method and Bayesian method for the estimation of degradation parameters and random failure threshold parameters. We conduct an analysis using a 14.5mm anti-aircraft machine gun as our subject. We obtain the estimated initial projectile velocities for a 14.5mm anti-aircraft machine gun under different projectile counts. We compare and analyze the prediction results based on the linear Wiener process prediction method, the nonlinear Wiener process prediction method, and the nonlinear Wiener process with random threshold prediction method. The method employed in this article yields a root mean square error (RMSE) of 367 and an average absolute error (MAE) of 309, indicating higher accuracy compared to the other two methods.