At the risk of being a party pooper, I must note there are (at least) a couple of matters that nobody has addressed.
Major issue: What reason is there to think the Army would add a third caliber to the system, solely for LMGs? When it was attempted circa 1970 (with the 6mm SAW), it was rejected by the leadership.
Minor issue: No one has yet proven that a belt-fed Grendel is even feasible. Yes, I know it ain't rocket science, but until one is actually built that works, it remains no more than a theoretical possibility.
Major issue: What reason is there to think the Army would add a third caliber to the system, solely for LMGs? When it was attempted circa 1970 (with the 6mm SAW), it was rejected by the leadership.
Minor issue: No one has yet proven that a belt-fed Grendel is even feasible. Yes, I know it ain't rocket science, but until one is actually built that works, it remains no more than a theoretical possibility.