The L129 from Lewis Machine and Tool, yes? This evolutionary dead end seems to be- NOT! How odd that the AR10 may ultimately be developed further as the AR15 begins to flowly fade.
Until they put a rugged side charging handle on them that you can stp on (if required) to clear a stuck round, I think I'll stick to the M14 platform. (If I was a right hander, then the FAL system would make sense, but it's definitely not LH friendly.)
If you want to imagine a funny scenario, imagine me shooting a BREN standing, LH, AND doing mag swaps and all, whilst on the move.