Swept-back propeller blades
Since WW2 swept back wings have enabled aircraft to fly faster. Sweeping back the blades of the A400M's turboprop engines could be because the speed of rotation would otherwise bring them into the high-drag region - straight props would possibly need a bigger "step-down" from the gearbox to stay well subsonic, which would have a weight penalty.
My 2 pennyworth anyway ...