This was my thought, considered Lee-Enfield since I would expect lots of Africa and elsewhere would have copious 303....Except that in 1920 the world was still more British than American. "Common calibers" were .455 and .303.
Even Indiana Jones ended up with a Webley by the third movie. And even in the first two, the revolver was his go-to. His backup was an auto.
I don't get the people picking the 1903 when there's better options. It didn't even take center stage in World War One.