So many different flavors of 7.62x51 NATO ball ammo that are close to being considered "match" where the consistency is way better than average.
Don't forget every barrel performs differently. What shot 1-2 moa in one rifle might result in 3-4 moa in another.
Here's what I've found over the years that were worth remembering.
Lithuanian (Headstamped GGG) 2003-4 (before they could put the NATO symbol on their cases)
Portuguese (Headstamp FNM) some years better than others
Austrian Hirtenberger (Headstamped HP) some years better than others
British Radway Green (Headstamped RG) some years better than others
DAG (German) Good ammo
MEN German) Good ammo
ADI (Australian) Good ammo
South African
Malaysian
Spain (Santa Barbara)
There are so many more.
Personally, 2004 Lithuanian shot the best groups for me out of a LRB M14 with 18.5" Criterion bbl. Nothing special about the rifle besides I love shooting it.
There's some great surplus ammo threads over at M14.com Here's one of the administrators experiences over the years
XXIV CORPS personal experiencesNone listed are corrosive. Good luck!