One thing I remember is that the majority of troops did not engage targets much beyond 200 yards even with their .30-06 Garands. They just didn�t think they�d hit much beyond that range and it was a waste of precious ammo to try. That makes me think the question of whether a .30 carbine could penetrate a heavy coat at 300 yards seem a bit moot. I'm sure someone will come up with a story of an exceptional rifleman shooting Chinese past 500 yards but the book covers the actions of the majority of GI, not the exceptional individuals.
I've read a couple books about the Chosin Reservoir campaign that repeat the claim that bullets from M1 carbines bounced off the Chi-Coms' quilted coats, but there was/is no real evidence of that happening.
It's possible that at the extremely low temperatures at that battle, some cartridges may have failed to ignite properly, I suppose... but I really doubt that a quilted cotton coat would repel even the lowly 30 Carbine bullet. I suspect that a lot of ChiComs were shot with carbines and failed to fall down immediately, even though they'd received serious GSW's.
But further to your post, it seems that most of the firefights that occurred in the Chosin campaign were conducted at very close range... the hilltop stand of Fox Company certainly did! Nobody had to worry about adjusting his point of aim for distances at all in most of those fights.
"I'm gonna have to science the schit out of this." Mark Watney, Sol 59, Mars
