Late 19th, with double action metallic cartridge revolvers. Some large caliber Webley, a Belgian "Bulldog", one of the European DA service revolvers.If you were currently limted to carrying firearms of a certain era (or replicas of that era), how early could you go and still feel "comfortable" about being armed?
For myself, I would consider the 1850s as early as I would want to go. This would provide me the choice of a Colt Dragoon, Colt Navy or maybe Remington 1858 as primary carry, and a Colt 1849 Pocket for a BUG or discrete carry.
Not ideal, but FAR from being unarmed.
I wouldn't think twice about being limited to guns from the pre-WW II time frame- I carry weapons from the 1900-1945 era frequently already.
Even better, once you start getting into the smokeless powder era.