The Mark I's were an attempt to give the ...
WWI troops a interchangeable semi-auto assembly that used a small .30 "Pistol" round for assaulting the enemy trenches.
Worked nicely, in training / development but never got made in sufficient numbers to the front.
All WWI rifles are the SA or RIA armory manufacture. Local the info on the
"low numbered" 1903 to avoid, questions about the heat treat used.
The 20' saw SA make low run and specials for trophy/match/ NRA sales, RIA was mothballed.
WWII was RA and Smith-Corona, with HS making barrels.