It’s basically the 6.5 Grendel, necked-down to 6mm (243cal), and will shoot a 105grain 243cal/6mm bullet.
The 6mm ARC is designed to run in existing in M4 rifle platforms.
I don’t know the velocity, but I suspect something under 3k. Barrel-length is an issue. An eighteen-inch barrel, maybe even a twenty-inch barrel, will likely be necessary to achieve reasonable ballistic efficiency.
Here we go again!
The 6.5 Grendel case (and this is a new case) doesn’t leave much meat around the cartridge head on the existing M4 bolt. One issue with the 6.5Grendel (in heavy use in the M4 platform) has been chronic bolt breakage. Maybe there is some new metallurgy, similar to what POF uses on their Revolution Rifle (7.62×51), but otherwise, I see bolt-life issues with this new round.
This new cartridge represents a ballistic performance improvement (improved range and penetration). No doubt. So does the 6.8SPC, which has been around and endlessly tested since 2004.
Despite all our conversations on this subject, I suspect DOD will be continually fielding M4s in 5.56×45 for at least another 10 years.
There are those who are naively seeking a single cartridge that will run in short M4s, but also render adequate performance in “designated marksman” rifles, sniper rifles, GPMGs, and also be available in both supersonic and subsonic versions.
Can we “have it all” in the same cartridge? It isn’t physically possible.
To convert existing M4s to 6.8SPC, or this new round for that matter will require a new bolt carrier group, new barrels, new magazines, maybe new springs and buffers. Even then, there will be inescapable start-up issues that cannot possibly be foreseen. There always are.
And, brass cartridge cases may be replaced with plastic! What could possibly go wrong?
The point is that this tardy update to the M4 rifle, even if it were implemented right now, is already thirty years late.
We desperately need a 300m auto-loading infantry rifle that shoots through-and-through things, and we haven’t had one since 1964. And at the rate we’re going, it will be yet another ten years before we get one.
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