While I agree breed specific bits are good, I was warned by the previous owner that curb bits, or any non-jointed bit, will make him rear and throw a fit, just not something he is into. She said he has been trained on jointed bits and doesn't like the hard bar on other types of bits. His issue I am having is that he wants to go where he wants to, and when I walk him in a circle to get his attention, he pulls "thru" the bit, and continues to go where he wants. So, I have a feeling he may need something with more "correction" to it, with my goal being to work with him and keep his mouth soft, and be able to get an instant response from him and do more of his neck reining and not need as much direct reining. Now that it is warm again I can get out and work him more than twice a week.
The issue at its most basic level is that your horse is out of balance and on his forehand, and you have little to no control over his haunches. Think of it in terms of a car...front wheel drive...what happens when the front tires lock? That's right...you end up in the ditch because you have no steering, the back of the car comes around and you're done for. What happens with a rear wheel drive vehicle? Even if the tires lock, you still can steer, it still responds to you.
Horses can stop or slowdown one of two ways. Youngsters, ill conformed individuals, out of shape individuals, ones with injuries and disease and the like, stop by using their front end. It's very harsh, heavy, as the front legs are designed as pillars, the feet dig into the ground, then they pop, then they dig in again and so on.
The other way, horses with uphill conformation, horses that have been shown how to use their bodies effectively, horses with natural self-carriage and the like, stop by using their haunches. They transfer weight rearward and coil the hind leg, which is structured like a spring. In this manner they absorb the shock of the transition. They can simply slide, or they can sit and turn and head off in another direction.
As a gaited horse, you have a secondary issue. To gait a horse has to tighten the back and hollow. A horse in this position can't engage their haunches. It's the main reason why people then go for the shanked bits...to try and get that control and steering back that they lose from the horse having to be hollow to gait.