Hydrocode simulations were used to directly improve and guide the design of an electrothermal research gun capable of firing small projectiles (0.25 g) at hypervelocity. The launch system uses an electrical arc and vaporization from a pointed copper anode with voltages up to 20 kV to produce a rapidly expanding gas as a propellant. The simulations were performed using ALEGRA with barrel expansion, projectile erosion, and velocity profiles as validation benchmarks. Guidance resulting from these benchmarked simulations led to projectile velocity gains of 30 . While the initial simulations reproduced and predicted the velocity profiles extremely well, significant erosion of the projectile occurred in the simulations that was not observed in the experiments. This was a direct result of Eulerian welding at the projectile-barrel interface. Several modifications to the simulations were implemented in this study to maintain the success observed in earlier velocity predictions while preserving projectile integrity to overcome erroneous erosion issues.