WinOP, im afraid you actually need 145% hit to be hit capped. Don't forget you can have hit food and other classes debuffs on the target (like the shadow priests Misery)
However, even with ICC25 Heroic gear it is impossible to get 145% hit so you can't remove misses altogether. The way to get a better hit vs miss ratio is to actually gem your gear with Spell Penetration.
Lot of people say Spell Penetration is for PvP only, but those people have no idea that bosses have spell resist as well. So you need to try for a balance of gemmed and enchanted Spell Penetration and Hit rating. Around 50:50 is perfect.
Also, make sure you are casting spells from behind. If you are in front of the target you will find that the enemy can see the Arcane Missiles or Arcane Barrages coming and will attempt to dodge them. The Expertise stat CAN remove these spell dodges, HOWEVER DO NOT gem or enchant for Expertise, as this will cause you to lose hit or spell penetration and you will start missing more from behind the target.