I have played the Game through on Normal Difficulty,and am now about to complete it on Delta Difficulty..I have experienced no problems in getting the TAC Gun to lock on to its Target,the Secret is to get fairly close to the Target,then your weapon should proceed to lock on,after you have destroyed the 1st of 2 of the Alien Ships main Armament make sure you vacate your position otherwise you WILL DIE instantly.I went right to the edge of the ships flight Deck in order to get my TAC Weapon to lock on...The TAC Weapon does not seem to have a great deal of range to it,so it could well be the fact that a lot of players are not getting up close and personal enough to achieve lock on.
