I agree with Mojjax. The keyhole on railroad locks is quite distinctive (the curved, "comma-shaped" hole). Keys and locks were designed so that any key from a particular railroad fit any lock. Therefore, there wasn't much variation throughout the years in the lock mechanism or keys. The locks themselves did change appearance though, and I would say that yours looks more like one from the 20's or 30's. Here's the real question. Are there any letters or initials stamped on it anywhere? (They would usually be on the bar at the top of the lock--the part that swings open when the lock is opened.) For example, "N & W" = Norfolk & Western, "VGN" = Virginian Railroad, etc.
