I have seen such references; most turn out to exaggerations. I want you to see a 1 x 18 sheet of paper at more than 300 yards -- let alone hit it. It is very difficult to shoot what you cannot see. And of course no optics! either spotting scope or telescopic sight. Indeed I'd like to see Col Chandler, long time USMC sniper instructor + author of Death from Afar, hit at 600 yards a piece of writing paper with iron sights and a modern gun with high velocity ammo [such as 30-378].
Here is the modern sizes of the scoring rings of 600 yard targets and these are round rings:
(a) MR-1 target -Enlarged aiming black for use in 600-yard matches only.
Aiming Black (inches)
X ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.00
10 ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.00
9 ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18.00
8 ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24.00
I personally witnessed an Army shooter fire a possible at 600 yards in 1974 at Range 4 at Quantico during I think it was a Regional Match and that means all his 20 shots for record were inside at least the 12 inch circle. He was using a NM M14 with NM open sights. (I was a Block Official at that match).
The same year I witnessed a NG shooter fire a 96- 4v at 1,000 yards with a standard issue M1 Garand and that was with standard sights, not NM sights.
Our requirements standard for THE Marine Corps Rifle Team in the mid 1980's was a ten shot group fired at 300 yards from our super expensive test rack and the group size had to be less than 2 1/2". This was from our double lugged, McMillan stocked, Krieger barreled M14 rifles. We had so many of them that went under a 2" group we almost made that our standard. I've also built NM Garands in that time period that would almost hold that group size. Now most of our shooters could not hold that tight of a group, but our rifles did.
I was a contemporary of and am still a friend of Norm Chandler. I was a Gunnery Sergeant when he was the XO of WTBN at Quantico, though I had known him for years before that.
My highest requal score with a standard service rifle was 249 out of 250 and that was with a perfect score of 50 at the 500 yard range, prone for ten shots. Though the target is a silhouette, you forget trying to make head shots and actually use the shoulders as an aiming point. The target was 40" tall (including the head) and 20" wide. My shots were all well within a 20" circle at that range and that was with a standard issue M16A2. Further, I am NOT a NM shooter and have never fired a round in NM competition.
Before I came in the Marine Corps, I could not imagine hitting something at 200 yards standing, but in boot camp I ran 7 straight bullsyes until I fired on the target next to mine. That was with a standard M14 rifle. I had grown up using shotguns and .22's but had never fired a high power rifle. So I realize how it would seem hard to believe until one see's it done.
Gus