Maximum Effective Range

[stanc]

Using the retained Kinetic Energy of that round, at 300 meters (538 ft. lbs.), as a parameter, I compare the following cartridges (all, based on velocites from 16" barrels): MK262, 77-grain, BC- 0.362, MV - 2650 fps.; .300 AAC Blackout, 125-grain, BC - 0.330, MV - 2215 fps; 6.8 SPC, 140-grain Berger VLD, BC - 0.487, MV - 2401 (NOTE: This load is approx. 5,000 PSI above the SAAMI 6.5 Grendel, and has a Cartridge Overall Length of 2.315" vs 2.260" for the Grendel); 6.5 Grendel, 144-grain Lapua FMJBT, BC - 0.636, MV - 2275 fps:

M855 - 538 ft.lbs. @ approx. 328 yards (300 meters);
MK262 - 538 ft.lbs. @ approx. 394 yards;
.300 AAC Blackout - 538 ft.lbs. @ approx. 388 yards;
6.8 SPC - 538 ft.lbs. @ approx. 760 yards;
6.5 Grendel - 538 ft.lbs. @ approx. 925 yards.

Unfortunately, that comparison has significant flaws in regard to the thread topic.

First, retained energy is not the criteria that determines maximum effective range.

Second, the 6.8 SPC and 6.5 G bullets are a lot heavier than would likely be used.*

The US Army currently uses lead-free (EPR) projectiles, as shown at right, below.




The heaviest EPR bullet feasible for 6.5 G is ~123 gr, similar to this EPR for 6.5 CT:





I think it more likely an EPR for 6.5 G would be ~105 gr, as seen in this lead-free bullet:


https://www.lehighdefense.com/264-match-...5gr-bullet



*Note the 0.449 BC of the 105 gr Flash Tip. More realistic than the 0.636 BC of the 144 gr FMJ.