Quote Originally Posted by akxx View Post
Very cool. Didn’t realize the 12” 6ARC would keep it supersonic to 1k. That is unique.

Not trying to start anything resembling a caliber war (and it doesn’t appear anyone took it that way)—genuinely curious what folks were looking to do with an SBR 6ARC (aside from the “just because” if you are also going with a longer barrel upper as well—I totally get that!).
You'll find that you'll want a bit more margin to assure staying sonic to 1K than 1147fps would usually permit. That's the speed output from a ballistic calculator, but you'll find that if you plug in cold and dry air, a high pressure system, some BC variation (normal even with great bullets like the ELD-Ms), that margin can disappear pretty fast and the sonic distance might fall even below 900y.

Which is not a knock on the 6 ARC at all. It's just a recognition that everything has limits.

The use case for the 6ARC (longer range paper punching and AR varminting) to me strongly suggests a 16" barrel. If you want shorter barrel performance/shorter range performance, I'd build a Grendel. A 130gr ELD-M at 2200 fps (doable in 12.5") will hit 1149 fps at 810 yards on the standard day.

And if you want to push higher sectional densities for very short range, the Grendel can go all the way up to a 156gr Lapua Mega bullet at ~1900fps, which is a Blackout-Crushing load in the sense that it is comparable sectional density as a 220gr subsonic 300BO, but at 1900fps instead of subsonic speeds. Again, not a knock on 300BO and sonic vs subsonic isn't really apples/apples.

Just pointing out that a short barrel Grendel has some particular attributes that favor short range use better than it generally gets credit for. The 6.5G is usually marketed as baby 6.5cm and guys are building comically long ARs trying to make it do what it just can't.

But drop it in to an SBR and some magic happens when you start to compare it to 300BO and x39 out of an AK.


I think the era of hyper-specialization is upon us, a product of the embarrassing riches of options we now have. Which means there is a place for both the 6.5G and the 6 ARC to coexist. For much of what the 6.5G was taken to be (a long range AR cartridge) the ARC is superior and will displace much 6.5G in that role. Which means the future of 6.5G depends a lot on people realizing its virtues as a shorter range do-all caliber. Compare a 12.5" Grendel with a 129g Scenar or 130 ELD you'll see that almost nothing a 300BO or x39 or similar can touch it in terms of energy and external ballistics from the short barrel.

Sorry so long.