After escaping Atlanta, Rhett Butler (Clark Gable) leaves Scarlett (Vivian Leigh) on her own so he can go fight in the war, before leaving, he gives Scarlett a Remington 1858 Revolver, which she later uses to shoot a Union soldier in the face.
The Union Soldier that attempts to steal from Scarlett's house is seen wielding a Colt 1860 Army, which was the Union Army's general issue revolver. Scarlett is also seen using one later on while trying to defend herself from a couple of homeless guys.
Ashley Wilkes (Leslie Howard) comes down the stairs before leaving to fight, a revolver that is hard to identify is seen holstered on his hip, more than likely it is a Remington 1858, seeing as it was the most common revolver issued to Confederate Troops.