Originally Posted by iridehorses
5 1/2" is a rather large bit. Are you sure that is the right size? A QH/Paint cress should not need a bit that large. How big is your horses? The largest bit I've ever needed was a 5 1/4" and that was for a 16.3h Hanoverian/TB cross that weighed ~1350 lb.
He seems to have an unusually large mouth. In a snaffle, I usually use a 5-1/4 which fits well. I picked up a "Myler" shank bit in 5" thinking it would fit. The main problem is the purchase rubs on the outside of his mouth when the shanks swivel. After very little use there was a visible rub. You can also see that the mouthpiece width is very snug.
Based on the amount of room, I am estimating that another 1/4 in on each side would do the trick, thus 5-1/2.
This horse is 16hh and weights about 1350lbs. He is built very "thick and stocky." His head is big and wide. By contrast, I have a 16.2hh QH that weighs about 100-150lbs less. While the size/weight isn't that much different, the QH looks much smaller than that paint just due to the build of each. The QH also uses a 4-3/4 to 5" bit, depending on the bit.
Now you have me thinking that maybe it was just the design of this particular bit. I will look around and try some others to see if a different 5" might do the trick.