Join Date: Jun 2017
Location: middle of nowhere
It depends on what organization's rules (if any) they are going by. In general, you'll be ok with a curb with a solid or jointed mouth as long as nothing extends below the mouthpiece. Some disallow anything with a gag action, which is what a jr. cowhorse is often technically categorized as.
For something similar, a 'dog bone' or 'colt bit' might be what you are looking for. They tend to have short shanks and swivel cheeks, and are relatively mild. For ranch classes, most people in my area show in a medium-port, fixed shank solid mouthpiece. If your horse will need to be ridden two-handed, though, in warmups, you don't want fixed shanks.