There was a great number of .303 & its derivatives after WWII up to the late 60's early 70's; so John I believe you are correct. I can recall a lot of the old 'outdoor' magazines that my uncle used to have that had been stored away; many of them mentioned at least one article that would pertain to the .303 in its many guises & lots of adds for ammunition to reflect as such.
As to the era between WWI & WWII, I believe it would be a real mishmash of 1892 Winchesters, 310 cadets & God only know what else! Most probably the common 12 gauge shotgun would have been the most common overall; the humble rabbit 'underground mutton' fed a lot of folks during the depression years.