If we're assuming that "game gun" in its original meaning refers to a British sxs used for shooting driven game . . . they needed to stand up to a lot.

But it's also good to remember that the Brits tend to take a "preventive maintenance" approach to their guns that we Yanks are less likely to do. (We wait until something breaks.) Traditionally, they'd send them back to the maker (or perhaps to a local gunsmith) after the shooting season ended. Whatever needed attention got it. A good approach with any gun that you shoot a lot--especially if it's an older one.