Wow!...I must be getting old. I'm seeing the 6mm ARC as Robert Whitley's recycled 6mm AR, or Greg Krebaum's 6mm RAT. Both were designed as Highpower Rifle Cartridges to be shot out of a standard AR magazine, and most often were shot out of a 26" barrel. Both were chasing 3000 fps with a 107 Sierra, and ended up blowing the shoulder forward to try to get there yielding the 6mm AR Turbo and the 6mm FATRAT. What made both feasible was the availability of quality 6.5 Grendel brass. Krebaum sourced dies from Hornady and so I suspect that's where Hornady got a clue to commercialize the RAT or AR as the ARC.

I have a Grendel upper and an AR upper, but I never put much time on them because I began hearing instances of cracked lugs in the AR15. I spoke to Holliger about the ARC when it first hit, and his response was tepid. He had the same concerns about exceeding the design strength of the bolt lugs because of his experiences with the 6mmAR and the RAT. John summarized his thoughts on his webpage if anyone cares to look.

I've got a bit more time on a 6mm WOA aka 6mm/6.8SPC, and it's a solid accurate cartridge, but doesn't have quite the boiler room of the .440 based cartridges. 107 class bullets also preclude magazine use. The 6mm HAGAR is a stretched out WOA with more powder capacity, but the same problem with feeding 107's through the magazine. ...but if you're looking to shoot these through a bolt gun...a WOA or a HAGAR might be your huckleberry.

The BR is also an option (I've got one). But the parts to build one were rare to begin with and have pretty much dried up...so mine is mostly a curio that I don't run hard.
[Linked Image from i.imgur.com]

Last edited by ChrisF; 04/18/23.