This video shows my concern with the standard Billy Allen curb bit. Even on a well-made model, such as this Professional’s Choice Bob Avila number, pulling on one rein transmits through the central joint and pushes the opposing shank forward. Does this bother the horse? Admittedly it doesn’t really seem to, and many horses do well in this kind of mouthpiece, but the two cheeks should be hobbled at the bottom to prevent too wide of separation between them. I’ve seen the same problem in similar bits, like the Imus Comfort models and others with a joint designed to allow independent side action, yet too tight to allow freedom of movement in other planes.
(I did own a very cheap TexTan Billy Allen at one point that maxed out this effect so severely that I ended up literally trashing it. The shank opposite the one I was contacting would flip forward and then get stuck in an upside-down position, and any efforts to fix it would only further twist it out of place, making an uncomfortable situation for the horse in addition to taking all control away from the rider. The moral of this story? Buy the highest-quality tack you can afford, but still inspect its actions carefully, lest they be different from what you had anticipated.)
This is a simple video demonstrating the actions of the O-ring and Western Dee. These are direct-action bits with no leverage and no mechanical advantage to provide amplification of force. They work on the tongue, bars, and lips of the horse, stretching the latter back as the rein pressure is applied. Thus, the cheek pieces of the bridle will be loosened as the bit is raised, and in extreme circumstances, the bridle can even fall off of the horse’s head if it is not well-secured. Therefore, it is always advisable to use a headstall with a throatlatch when riding with a snaffle bit.
The loose ring bit has rings that slide freely, as its name suggests. This allows slight “jingles” of the reins to be felt more easily by the horse, which can allow for subtler cuing, but some horses do not appreciate the “noisiness” of this bit. Also, there is some risk of pinching if the lip gets caught between the cannons and the cheeks. The fixed ring bit is more stable in the mouth, and in addition, its flat sides push against the outside cheek and provide some outside lateral pressure when the horse is asked to turn to the side.
These particular bits both have a two-piece jointed mouth. The O-ring has a twisted mouthpiece, making it more severe as it rubs against sensitive tissue. These single-broken mouthpieces will fold in half as the reins are pulled, collapsing onto the tongue and bars. It has long been said that there is a “nutcracker” effect, where the middle point of the bit pokes into the horse’s delicate palate. However, it has been shown by Dr. Hilary Clayton’s research team that this effect is much exaggerated, and most horses will more than compensate by retracting their tongues, so that the palate is never contacted.