I don’t doubt the general veracity of the story, but I wonder if the ranges cited are accurate. I mean, you could take someone who has never handled a rifle in their life to the range and they’d be able to hit man-sized targets at a hundred yards.
Back in the late 1960s to late 1970s, USMC Rifle Ranges started at 200 yards. 10 rounds Standing Slow Fire, then 10 rounds Standing to Sitting Rapid Fire (5 rounds per magazine). Target is a 12” Bulls-eye - 5 points
Move back to 300 yards. Again a 12” bull. Slow Fire -5 rounds Kneeling, 5 rounds Sitting. Rapid Fide - 10 rounds Standing to Prone.
Finally, at 500 yards, 10 rounds Prone Slow Fire at a 20” Bull. Once the Corps transitioned from the M-14 7.62 to the M-16 5.56, the 20” Bulls-eye became a 20” wide Silhouette.
One Marine recruit in my platoon shot a 241 of a possible 250, dropping 3 points at each of the Slow Fire positions.
The Marine Corps thinks quite highly of marksmanship.