New Army "Caliber Configuration Study"

[stanc]

LDAM is supposed to replace .50 BMG in the anti-personnel role...

That is not what Guardsman26 said: "[LDAM is] envisioned to replace the Medium Machine Gun and possibly the HMG (.50 BMG)."

Also remember that before Afghanistan, 7.62mm MGs were not carried by infantry squads...

So what. Pre-Afghanistan is no longer relevant.

I envisage CLAWS - and the GPC - replacing all of the 5.56mm weapons and also the lightweight 7.62mm MGs and DMRs. LDAM would replace the heavy 7.62mm and the .50 cals in the support role.

Yes, that's mostly the same as what Guardsman26 reported the US Army envisions for CLAWS and LDAM (except for the uncertainty of LDAM replacing the .50 HMG).

It would provide a common cartridge for all soldiers with rifles (except snipers), and for all soldiers carrying portable MGs...

That's evading the point. The notional GPC does not provide a common cartridge for the weapons squad, infantry platoon, company, and battalion.

And since when isn't the .338 LWMMG a portable machine gun?