Being this is so early,
Makes you wonder if this isn't just a 'Template' that is tweaked later on after......... I'll say: more experience was gathered from the newly introduced M1carbine.
When I read TM 9-1276 from 1947
Page 36-
Rifle bore cleaner is the suggested method for bore cleaning.
But if not available the bore may be cleaned
with a solution of
1/4 pound of castile soap or issue soap shaved into
1 gallon of hot water, or a solution of
1 1/2-tablespoonfuls of soda ash
to each pint of hot water.
Seems TM 9-1276 is my most often used reference:
http://www.90thidpg.us/Reference/Man...-1276_1947.pdf
Lessons learned with more experience, I'll assume.