Mare in question (or perhaps, hony/pony) is heavy and hard mouthed. Now, I'm not one to just jump into a bigger bit, that's NOT my goal at all. In fact, I've spent a great deal of time (a couple years) working on this mare's acceptance of the bridle. She was, when I got her, an overused polo pony who had some pretty gnarly things shoved in her face.
Right now I have her in a copper mouth eggbutt, which has been the winner so far. I have ridden her in my full cheek before and preferred that over the eggbutt, which is why I'm looking at the fullcheek in the link above.
I've always been a big believer of "if you don't know the mechanics of the bit, don't use it". So I'm at a loss. I'm a simple snaffle girl, or only have knowledge of the other bits, like pelhems and hackamores, that I've used (which neither of those, IMO, would work for my mare).
My small experience with Dr. Bristols wasn't fun, I hated them and am not keen on attempting it again, though like I said, minimal experience.
I've never used a bit with a roller before.
My next go to was something like a slow twist.
Any input would be helpful here. I'm starting to pull my hair out. This mare has been doing fabulously, but I feel like I'm at a turning point in her training and I don't know where to go from here.
The joints of the center piece on the Stubben EZ control are designed to not collapse at all when pressure is applied. If the horse is carrying the bit softly, it has a little bit of play. If the horse or rider pulls, it basically turns into a solid mullen mouth. As soon as the pressure is released, it softens a little bit again.
I'm not a huge fan of mullen mouth bits for a tough-mouthed horse as I feel it is easy for a horse to lug on them, I tend to go with a regular French link or a lozenge link for the extra play in the mouthpiece. Maybe just a regular French link full cheek would work?
I had no success with this bit. All it does is lock up into what is essentially a mullen mouth. Last time I checked, if you need control, turning a 3 piece jointed into a mullen doesn't really give you more control. I have a freight train type horse and he just said "golly gee thanks" and hung on it. There was no control, let alone "EZ" control. So far we have the most success with a pelham or waterford. I was surprised he did, but hung right on the Dr. Bristol.
I have one with a loose ring. I liked it when I first tried it, but I'm still deciding if I like it. If he is in the right mood, he goes great in it. But I'm also noticing that my horse tilts his head in it more. He doesn't do that in his 3 ring Watson bit that I use for jumping, so I'm sure it isn't physical. I can't decide if it is his latest form of evasion or something encouraged by the shift of pressure to the bars of his mouth.
A slow twist, and if that doesn't do it, progress to a waterford.
I bitted up for winter-horse from a plain D to a slow twist D. For about a week he backed off it a little too much and was a little displeased with me but he's gotten over it and is working absolutely beautifully now.
i loved this bit on the young horse i was riding because it was solid enough for her to learn contact and keep her from playing with the bit too much (she was a chewing machine in a normal 3-piece), but still had a little bit of play. that said, it doesn't sound like it will help you very much.
I have an EZControl and I like it. I bought it for a gelding that had trouble taking contact, and with the EZControl he is much more willing to keep a feel of the bit.
In my horse's sake, he was wanting to curl behind to avoid contact, but this is a symptom of a similar problem; horse not wanting to take contact...yours is just going about it differently and opting to lock the jaw rather than curl.
I DO think it is worth trying to see if your horse's issue comes more out of fear of the bit rather than being a bully. I could see a horse wanting to lean on it, but leaning is corrected with leg, not with bits, so I wouldn't see that as being an issue this bit would create.
I would also like to suggest a figure-8 noseband; I had a freight train mare who was being ridden in a super thin, straight bar snaffle with her old home, and still semi-out of control...the issue was the mare was just so sensitive, the she locked her jaw to protect herself! She also had fat cheeks and would bit her cheeks if she relaxed her jaw (cavesson pulled her cheeks into the teeth). She went much better with a softer bit and the figure-8...presumably because she no longer felt the need to lock up and protect herself.
I went ahead with the slow twist (they had an eggbutt which is what I bought) and rode her today and she was lovely, I only rode her for about 10 minutes as she worked pretty hard yesterday and I just wanted to test run the bit, but from what I can tell she went really well in it. really well.
Not ruling other bits out, but so far, this one is the winner.
I wish I could find a place to try the EZ bit (or, any bit, really) without forking out the cash because they're a little spendy :/ I'll keep an eye out at the used tack shop for one.
for fun, here's a picture of the mare in question... just because I think she's lovely. She's not built super uphill, so that's where a little of our problem comes in. This might be where the boucher could come in handy.