During the scene at the 415 building in NY, Bourne has Dr. Albert Hirsch held at gunpoint in a small room. They are discussing Bourne’s past. If you watch the weapons close they change after a flashback. Originally Bourne is pointing a Glock without an external hammer at the doctor. The flashback occurs, and when he comes out of it he has a Sig Sauer with an external hammer pointed at the doctor.