Can you ride him in a smaller area?
If he where mine I'd ride him in the round pen, ours is about 20m. Trot him out for a while, then ask him to lope in a 10 or 15m circle. It's going to be pretty hard for him to gallop in such a small circle and its going to tire him out pretty quickly. If he can only do one circle or half, great. Break him down to the trot and the walk. Then rest again, another circle of loping. Try to make 1 circle into 2, then 2 into 3 and then eventually 3 into a lap around the round pen and then a few laps around the round pen. Graduate to a small arena and keep working up.
I cannot stress how important it is to keep things calmmmmm. If he cannot trot or walk on the end of the reins calmly THAT is where you need to start. Make sure when you ask him to lope your doing it gently, not "slamming on the gas".
If you increase the "size" of your bit this time it will only be a matter of time before you need a "bigger" one, then another "bigger" one after that. Fix it now BEFORE you really NEED those bits to control him. It won't be long until your riding in the bits pictured above.
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