..the British introduced in 1917 'Green Label' (or 'Green Cross') .303 ammunition specifically for synchronised guns. This was taken from standard production lines, but carefully selected from batches which complied with tighter manufacturing tolerances and gave reliable ignition.
Still relevant today, modern sniper ammunition as used by the British army is standard production ammunition, it is the first batch of ammunition made from new forming and reloading die's, the tighter tolerance is due to the tooling being brand new, nothing more.