If GySgt Hathcock (bless his departed soul) really did use a center hold with a post front sight on round bullseyes, he's the only top classified shooter I know about who does. If I knew that when I shot with him at the 1971 Interservice Matches, I'd sure have asked him how he was able to hold elevation so well.
A center hold's never worked well for post front sights on round bullseyes. It causes too much vertical shot stringing 'cause it's hard to see were the middle of that round fuzzy black ball is when your aiming eye's focused sharply on the front sight post. 6-o'clock hold's easier to put at the same elevation time after time after time on the bullseye's bottom. The post typically shoots best when it appears as wide as the bullseye; windage holding errors are minimized this way.
And marking a service rifle's front sight with some other color is an external modification and ain't allowed for NRA and CMP sanctioned service rifle competition. Saw a guy disqualified in a leg match for the white dot he put on the rear bottom part of his M1A's front sight post. The front sight can be different widths, but that's all; has to be otherwise unmodified.
The above aside, many folks have painted marks on their rear sight knobs so it would be easy to tell when they were at zero; especially on the windage knob of an NM-2 half minute rear sight on M1 and M14 rifles. Someone challenged a member of the USMC Reserve Rifle Team for his M14NM's rear sight having red marks on it. The referee told the challenger that was just the same as Firm Grip being externally applied to the butt plate; another external modification that didn't matter and was not explicitely disallowed in the rules. Go figgure that out.
US Navy Distinguished Marksman Badge 153
Former US Navy & Palma Rifle Team Member
NRA High Power Master & Long Range High Master
NRA Smallbore Prone Master
Last edited by Bart B.; February 6, 2013 at 12:41 AM.