So, if my lifestyle choice is 11-12”(ish) AR-15 barrels and shooting factory ammo at thin skinned animals out to 300 yards......
Does 6 ARC do anything better that 6.5 Grendel?
For instance, I’d be completely content if someone told me the whole damned thing is a wash, but recoil is noticeably less.
Both are good choices, but the 6 ARC will give you a little less recoil and a little flatter trajectory. Saying this despite the fact that I really like my 12.5" 6.5 Grendel.
Energy numbers don't mean that much compared to choosing a bullet that works within the velocity window you'll be using. It doesn't matter if you've retained 1,000 ft-lb of energy if the bullet is only doing 1700 fps and needs 2100 fps to expand; it won't effectively deliver that energy in a soft target.
The Grendel has at least one really good choice there (the 129gr ABLR that functions down to ~ 1400 fps) for short barrels but starts off pretty slow so the velocity window is small and short with many other bullet options. I think the 6 ARC opens up that window by starting off a little faster. Depending on your bullet weight and load, with a 12" barrel you're looking at 2200-2400 fps for 120-130gr 6.5 Grendel, and 2400-2550 fps for 95-105gr 6 ARC, as best I can tell. I'll be spinning up my own 12.5" 6mm in the next few weeks for the same reasons, already have a couple other barrel lengths to go with it as I've posted about here.
Ammo cost is a consideration of course, but most 6.5 Grendel ammo isn't very cheap either. The one exception I know of is the 100gr Wolf FMJ load, which actually shoots respectably well in my short Grendel (it'll maintain consistent body shots at 650 yards, and head shots most of the time). Some people report poor accuracy with that load though, so YMMV. I do shoot long distance with my short 6.5 Grendel, mostly with the 123gr ELD, and it does work, but you have to account for a LOT of drop and really have your distance and muzzle velocity dialed in correctly.
I can say this for sure - if I didn't already have a 6.5 Grendel, I wouldn't bother with one at this point, I'd just do the 6 ARC (or one of the other 6mm Grendel variants that I've been loading for a few years, same effect either way). I think it's what the 6.5 Grendel should have been to start with; it offers better trajectory and isn't hampered by depressingly low muzzle velocity.
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