'The Whole Nine Yards'
Centre to centre the disintegrating link for the .30-06 Browning measures about 12mm. This gun, re-chambered for .303 British was the M2 used in the Spitfire etc. The belt pitch may well have been slightly wider, to accommodate the rimmed cartridge, but not massively so. So at 300 rounds per gun, we have 3.6 meters / 11 Ft 9 3/4 in. Way short of the 9 Yards / 27 ft.
That tends to limit the discussion to turreted weapons with belt feeds, looking at the figures a thousand round belt of some other ammunition, slightly narrower would fit the numbers, and belt make up would have been done with bulk supplied rounds to a standard length. I always sort of assumed that the phrase was American, so I would have expected .30-06, can anyone do a check on .50, maybe a 500 round belt.
PA-28