A Butterfly cheek has a snaffle setting (top ring) and a curb setting (bottom ring). Snaffle actually refers to the "location" the rein is attached, not the mouthpiece. It is a common misconception, with a lot of people referring to "snaffle" as a single jointed mouthpiece. You can have a mullen mouth snaffle or a mullen mouth curb with leverage. You can also have a single jointed curb as well (although I don't recommend that bit for any horse...
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So what I am saying is that you can try to put the rein in the curb (or lower) ring on the Butterfly. Just be careful doing it if the horse is really light mouthed.
I would think so. You may also want to try to "change it up" to give him something else to think about besides the bit, especially before he gets his tongue over. Show him some obstacles, set out some cones to drive around, get a thick piece of plywood or an old rug to drive over. If they are bored, they are more likely to fuss when they are learning to carry the bit. And the steering will get him used to the bit in the meantime. Just make the obstacles wide and flowing.
Latex can work for some horses, but with small horses, you have to make sure the mouthpiece doesn't get too thick.
He needs to learn to carry the bit on his own. I am not a big fan of "contraptions" to keep the horse from doing something. What happens once you take it off if they haven't learned to hold the bit? You are back to square one.
Myrna