He is currently in a full cheek snaffle but he is still able to nap/bolt off when trying to circle making it tricky to school! He can be strong too. What other bit could help me with steering?
Sounds like he's trying to tell you something - especially as napping and bolting are two very different evasions. An instructor or some other professional is a good idea. I would also be wondering about tack / teeth / back. Upping the ironmongery is not the best first choice I'm afraid.
When he is napping you need to ride in a defensive manner, start riding horse strongly forward well before you get to the point where he naps. Look beyond the point he naps, turn your upper body if need be and don't look at the napping spot. Keep the contact on both reins and carry your whip on the outside and use it on the shoulder to stop him pushing it out. To nap.