I stumbled across a US Army training film from 1943 titled: "Rifle Marksmanship with the M1icon Rifle - part 2" and a couple of things jumped out at me.

I thought lockbar sights came on the M1 in WWII, but the rifle in the film looks to have the T105 style...and the gas tube appeared to be in the white.

When did they start using the T105 sight?

were the gas tubes hard to parkerize? (I just thought mine had the finish worn off)

Jim