yep, its a .303 British.....and cartridge with a grand history in both warfare, and in the hunting fields. Not punishing to shoot either.
Tiki, my answer was based on rifles typically encountered in the american market place (here at least) I have never seen a British made Mk1 with a flip sight, in decades of looking at Enfields at gun shows, buying them myself and having friends buy them.(american shooters prefer the more elaborate sights) And tend to take those flip sights off very quickly,
and would hardly ever put a L flip on to replace the better ones....we hate them in other words)
Yet somehow the long branch and Savage made guns tend to keep thiers, and encountered 50% of the time with the flip.
So here at least its going to be one of the two makers.(99% odds)
Lighten up Francis!.....;Actor Warren Oats, in the movie "Stripes"