02-11-2013, 08:53 PM
LRRPF52 Wrote:If you're relying on just BC and trajectory comparisons, the 16" Grendel currently beats a 16" 7.62 NATO L129A1 or SCAR-17 for wind drift when pushing the 147gr M80, assuming a 2450fps speed for the Grendel, and a 2620fps speed for the 16" 7.62 carbine (7.62 NATO M80 varies in 16" guns from 2550-2620fps).Trouble is, you're comparing 7.62 FMJ Ball to 6.5 HPBT Match. Hardly a fair comparison.
The 7.62 NATO at such low speeds for the bullet will not fragment at CQB (bad), and has the following drop/drift at 4400ft ASL (thinner air like A-Stan)...
Drop at 600yds: 4.6 Mils
Drift at 600yds: 1.4 Mils (10mph full value wind)
At 2550fps mv, it is:
600yds: 4.9 Mils
Drift: 1.5 Mils
The 16" 6.5 Grendel with current civilian factory 123gr at 2450fps:
Drop at 600yds: 4.9 Mils
Drift at 600yds: 1.2 Mils
The Grendel does that with 50% less recoil, much less ammo weight, less ammo footprint on the soldier's load-meaning more capacity to space. The energy difference at 600yds is 847ft-lbs for the 2550fps M80, and 763ft-lbs for the 2450fps 123gr 6.5mm.
Try the calculation again, with 6.5 FMJ 120gr, 0.420 BC.