"After the USA pulled out of Vietnam the USMC had made the commitment to continue their sniper program during peace time and they continued to improve their equipment. The US Army, on the other hand, had once again disbanded their sniper program at the cessation of hostilities and it was the marksmanship units that had to lead up the pursuit of better equipment for the Army. These various military types met at a symposium and agreed that something had to change and it was widely accepted that what was referred to as “Mexican Match” ammunition was a far better ammunition than M118 Match ammo. ‘Mexican Match’ was made by using military 7.62 brass and loading it with the Sierra 168gr Match King bullet.
The name ‘Mexican Match’ reportedly came about because the first time this load was used was during the PanAm games in Mexico City. The accuracy improvement over the M118 Match ammo was remarkable, often shooting as much as 50% tighter groups. Because of these results a new load was developed called the M852. The design was simple, put the 168gr Sierra Match King bullet on the same M118 brass and powder. The M852 was adopted in the early 1980’s and was for match use only. Because the Sierra Match King (SMK) bullet had a hollowtip as a byproduct of production, it was not regarded at the time as being acceptable for combat use in terms of abiding by the Laws of Land Warfare. Since the M852 was the new match load for competition use, the M118 was redesignated the M118 ‘Special Ball’, or SB, and was the authorized ammo for combat use by snipers."
From:
http://www.snipercentral.com/history-m118-ammunition/
