04-26-2011, 07:23 AM
To match the long-range (up to 1,000m) performance of the 7.62 M80, in terms of retained energy and other metrics, with a smaller and less powerful cartridge requires a bullet with a better ballistic coefficient than the M80's. The 123 grain Lapua Scenar seems to do that job very well in the Grendel, so it's a matter of getting close to the BC of the Lapua with a mass-produced FMJ military bullet.
As far as 77 grain 5.56's are concerned, I have the strong impression that no calibre smaller than 6.5mm is likely to prove acceptable as a replacement for 7.62mm, in terms of penetration and terminal effectiveness. The Chinese tried to make a universal cartridge with their 5.8x42 (in light and heavy loads), but their army is hanging onto their 7.62x54R MGs.
As far as 77 grain 5.56's are concerned, I have the strong impression that no calibre smaller than 6.5mm is likely to prove acceptable as a replacement for 7.62mm, in terms of penetration and terminal effectiveness. The Chinese tried to make a universal cartridge with their 5.8x42 (in light and heavy loads), but their army is hanging onto their 7.62x54R MGs.