"I read that the pre-war M1 rifles had raw linseed oil for a finish, and when rapid-fired would heat the oil on the lower handguards so much it would char the walnut or even catch on fire."
You are correct. Both Springfield and Rock Island held the finish machined stocks in a tank of heated raw linseed oil until "saturated". Then hung by the tang screw hole over night. What wasn't dry had the rifle assembled as it was. The problem became that the individual soldiers then used turpentine to buff down the excess goo on a new rifle (a new one each time you re-enlisted). Then they hand rubbed a coupe of drops of "boiled" linseed oil into the stock every Friday afternoon before Saturday morning inspection. The real killer was the guys that "cheated" and mixed Johnson paste wax (from floor buffing) with turpentine for a really fast shine to the wood. '03's would just smoke the handguard at the range, but the early gas trap M-1's would melt the linseed oil, boiled linseed oil, turpentine and paste wax and ignite the front handguard.
