The premise that 6.5 Grendel is capable of replacing 7.62 NATO as well as 5.56 NATO was originally based on ballistics data of the 123gr 6.5 Scenar match hollow point versus the 147gr 7.62 M80 full metal jacket loads.
Since that time, the US Army adopted the lead-free M80A1 to supersede the lead-core M80, thereby rendering conclusions based on the Scenar/M80 comparisons of little or no value in determining if 6.5 Grendel is a viable option for a General Purpose Cartridge.
If 6.5 Grendel ballistic superiority depends upon having a projectile weight of 123 grains, this creates some issues in switching from lead-core to lead-free projectiles, due to the increase in bullet length necessary with the lower-density materials used (steel and copper).
The lead-core, 123gr Scenar is itself rather long (1.3"), and eats up a significant amount of powder space in the cartridge case as a result (below, right).
Muzzle velocity of a 123gr bullet from a 16" barrel is very modest, only 2350 fps for the Hornady 123gr SST load. http://www.hornady.com/store/6.5-Grendel-123-gr-SST/
A 123gr lead-free projectile of the M80A1 type (below) would be at least 1.4" long, if not longer, further reducing powder capacity. Which would presumably have a negative impact on muzzle velocity, trajectory, wind drift, and terminal effects.
The alternative is to opt for a shorter bullet, that would have minimum extension into the propellant space. Shorter equals lighter, which -- together with potentially greater powder charge -- means muzzle velocity would be much higher. Unfortunately, shorter and lighter also means lower BC, which adversely affects ballistic performance.
So, the question is, what would be the best weight for such a 6.5mm lead-free projectile, so as to achieve the optimum balance of ballistics and terminal effects, and would its performance be good enough to be a viable replacement for 7.62 M80A1?
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