Miniguns usually only have 6 barrels, the GE Six Pak had 6 barrels (obviously), the GAU-19A was 3 barrels, if I recall correctly. My memory is a little fuzzy but I seem to recall the minigun in second edition resembling the GAU 3 barrel triangular setup.
In any case, you're just porting the barrels at the right angles to bleed off excess gas to reduce felt recoil (also bullet velocity but that's not in the rules). Anyone doing that should be charging by the barrel, they could, but RAW the wouldn't have to.