What is it about 6.5 Grendel owners that cannot accept that it is no longer 2002?
I hear it repeatedly, "6.8 is just 7.62x39 for an AR." Um, no. Especially since it was specifically designed to out reach 7.62x39. At 400 yards the drop from an AK is about 54"; the 6.8 is about 35". To put that in perspective, with an AK I'd have to aim nearly an entire person above the target to hit center mass. The 6.8's drop is comparable to the 77gr Mk 262 at this range. Gee, is Mk 262 just a ultra-light 7.62x39mm round for the AR? Even more fun is some 6.8 loadings are carrying 50% more mass at the same velocity as the Mk 262 at 400 yards.
Some numbers:
AKM firing a standard 123gr 7.62x39mm round has 2,300 fps (1,444.6 ft/lbs) at the muzzle and 1,324 fps (478.7 ft/lbs) at 400 yards.
16" barrel 6.8 AR firing a 115gr Sierra Match King has 2,650 fps (1,792.9 ft/lbs) at the muzzle and 2,143 fps (1,172.5 ft/lbs) at 400 yards.
See? Not 7.62x39mm at all. More energy at all ranges, less drop at long ranges.
I think it comes from the mediocre loadings from Remington in the way back. That was also when SAAMI spec chambers and 1:10 rifling were the norm. The Remington loads were loaded 200-300 feet per second slower than current standard ammunition.
Virtually all 6.8 manufacturers have changed to the Spec 2 chamber and 1:11 rifling.
Another gigantic problem with internet debate on cartridge performance is utter faith in online ballistics calculators and a complete absence of measured data. If you plug the 6.8's muzzle velocity with a 115gr SMK's numbers you don't get 2,143 fps, you get 1,669 fps (711 ft/lbs) at 400 yards. That's STILL more energy than a 7.62x39mm though...
Grendel owners, put down the Kool-Aid and do some research before you go off about the limitations of 6.8 as it compares the 7.62x39. Perhaps it was true against the underloaded Remington ammunition eight years ago; since then a lot has changed. Refusing to acknowledge that change is making you look foolish (at best).
By the way, if you want to see a real "7.62x39mm for the AR" check some supersonic loads for .300 Whisper or the forthcoming .300 AAC Blackout.
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Frankly, at 400 yards I'd much prefer .308 NATO or something in that general vicinity...I've always thought that ARs were meant for closer-in work.
ReplyDelete400 yards was used as an example range because numbers for all rounds compared was readily available.
ReplyDeletePast 150m the M16A2 firing the M855 round loses the fragmentation that 5.56x45mm NATO needs to be effective. 6.5 Grendel and 6.8 SPC don't rely on fragmentation for terminal effect, so they both still work out at 600m (just like 7.62x51mm NATO). 7.62 NATO carries more thump out to 600, but there's a mass penalty. For example the FN SCAR H is 0.6 pounds heavier than my 6.8 AR and gets five fewer shots. I think that 6.8 carries enough thump to 600m to take advantage of the extra shots.
A nit: It's 7.62x51mm NATO, 7.62 NATO, .308 Winchester or .308; it's never .308 NATO.