While this debate has raged through the decades, flaring with every significant improvement and/or change in firearms design and ricocheting off of every military contract and police department purchase—the subject has grown even more complex of late, due to the introduction of dedicated M4/AR-15 cartridges such as the 6.8 SPC, 6.5 Grendel and .300 Blackout.
Yes, I know: Many deserving carbine cartridges such as the 7.62x39mm want in. And sure, some of them will leave size-14 combat boot-prints all over the cartridges just listed. But much as I deplore the necessity, let’s confine this discussion to rounds in one arena: those appropriate for the M4/AR-15 family. Otherwise this article would turn into a book.
Trouble is, each popular carbine cartridge has significant strengths, especially in certain areas. What will work best really depends on you and your shooting abilities, your environment and lifestyle, and the probable demands those unique elements will place on your carbine.
Here’s a close look at the strengths and weaknesses of a handful of the best AR-15 cartridges available on today’s market. Only you can decide which is best, so be sure to vote for your favorite.
<h2>6.8 SPC</h2>While I’ve never personally drunk the 6.8 SPC Kool-Aid, a lot of very knowledgeable shooters have. It’s second only to the 6.5 Grendel—which is a much less available round—in gap-bridging performance. While it doesn’t shoot as flat as a 5.56mm or hit as hard as a .300 Blackout, it hits quite a bit harder than the 5.56mm. It also shoots notably flatter than a .300 Blackout, punching a 110-grain Hornady V-Max out at 2,550 fps. Significant body taper enhances reliability under hot and dirty conditions. <p></p> On the con side, the 6.8 SPC doesn’t feed reliably through standard M16-type magazines, no matter what enthusiasts claim. Some mags work; some don’t. You’re best off with magazines designed specifically for the 6.8 SPC. And whatever you do, don’t call it the “.270 Short” and boast that it offers performance just shy of the classic .270 Winchester big game cartridge. It’s a runt in comparison—don’t insult the legend.