At the beginning, while in Egypt, the professor's assistant shoots to the aliens with a full-auto Mauser C96 pistol. Well, we are in 1914 and this pistol was produced only in 1932. And more: no full auto pistol was in production in that year or before. Back to the future!
You're wrong!! The gun used is a Mauser C96 Parabellum made in 1915, which is still a year off. The gun made in 1932 is a C96 Broomhandle. It has a long wooden stock and measures around 22 inches total.