It should be noted that the regular rifle-butt/pistol-whip melee can still be performed depending on your proximity with the enemy when pressing the melee button. The easiest way to do a regular melee is to press the melee button and walk into the enemy, rather than getting into brutal melee proximity and pressing the melee button. It might take some practice to time the distance correctly, but the regular melee can be very useful as it kills the enemy in one hit just like the brutal melee, but takes much less time than a brutal melee, keeping you less vulnerable on the battlefield.