The 100 yard national records were set in 1987 at NRA registered compititions. The target has a 1 inch x ring to break ties, and a 2 inch 10 ring. All shooting was from a prone position with no artificial support.
The standard course of fire is 40 shots fired in 2, 20 minute strings.
The record for iron sights is a perfect 400 with 39 of the 40 inside the X ring.
The record for the any sight match, which alows a scope, is a perfect 400 with all 40 in the X ring. To set the record as high as possible the shooter went on to fire another 40 into the same group. That is 80 straight shots into a 1 inch group at 100 yards.

My personal best on that course was 389 with 19x. That was a long time ago.