the 6mm ARC’s

Hmmm... so this will work in a standard 6.5 grendel or will it be too much for it and require a new barrel?

The Hornady 6mm ARC is a short-action cartridge designed to push the limits. Based on the 6.5 Grendel cartridge case, the 6mm ARC was designed to achieve comparable ballistics to the AR10 308 WIN, all while operating in a 30% lighter system.

CMMG Announces New Rifles Chambered in 6mm ARC

Barrett Announces Shipment of 6mm ARC Rifles to U.S. DOD

Brownells Unveils Exclusive Products For New 6mm ARC Cartridge

 

Upper complete.
Or BCG and barrel.
And Magazine

 

Just barrel,bcg and mag are Grendel.
It is a 6mm Grendel.

From a 223 it would require a barrel,bolt and Grendel mag.

 

thing is if you have a grendel upper do you need to make any changes for the ARC?

 

YES.
The chamber is different so a new barrel is required.