Heh. The Belgians kept working on the BAR, added bits from some other guns, turned into the MAG58 and sold it to the US in 1977, sixty years after Browning sold them the first version and replacing the M60 that replaced the Brownings. Victory! And an illustration of what the Ordnance Dept could have done if struck with a clue stick.I'm not sure what you think I'm arguing, but I'm not stumping for the US Army WW2 BAR. My initial point was that it was generally controllable due to the weight, not that it was particularly reliable or a great option compared to it's competitors. The core design was fine, as the Belgians were able to demonstrate with upgrades...thing is the US military decided not to actually make their version better. An improved version could have been workable is all I'm saying.
Personally I think the most likely route of getting the WW2 US to an intermediate cartridge is via the SMG/Light Rifle channel. Have some bright spark suggest a select-fire weapon in a light cartridge that covers both PDW and close assault requirements (.22 Spitfire?), Ordnance want it powered up a bit more in case the enemy is further away, and whoops you have 5.7x48 or something loaded to rifle pressures in a weapon which is good enough for most tasks on the battlefield.