OK - I get it now. Lets see if any of this rambling makes a lick of sense.
The trail bit is really a curb bit designed to be ridden off contact (loose rein) and neck reined. It's too much in play to be ridden on contact. It would work on barrels, I'd think, (what do I know about barrels) but you'd have to be gung ho enough to ride it loose and rein only for turns.
The full cheek snaffle ought to be a good turning bit, it's what they were made for. But you would want to ride it on contact, and turn him by bending him with it. Yes, it'd be a more exaggerated, and more steady pulling kind of input. If you just try to pop it, like you do probably can with the curb... you won't get the same response.
Do you really want a ~bend~ in barrels? It seems to me when I've seen barrel turns they are more of a pivot than a bend. There is something that would conflict between the on contact soft bending neck a dressage rider would want using a snaffle and riding with a tie down where they are actually encouraged to lean on it. Leaning on it by it's nature stiffens the neck, which makes them unable to also simultaneously bend sideways with the cheek snaffle. They're gonna want to stay stiff and straight and pivot. You might as well have the curb bit on.
I really don't know barrels from bananas, I'm just thinking through how the machinery works.
The way I have been taught is you want them to bend around not pivot:) but you can get too much bend. Also you want the bend in their bodies, not just their neck which is a common mistake that alot of barrel runners make. You do not want your horse swinging his butt out as he goes around the barrel which, I think, is what would happen if the pivot. The back end should follow the same path around the barrel as the front end went.
Your description of use of reins with my trail bit is where I get confused. I do two hand with that bit. I have always been under the impression that with any broken bit you can two hand as each side of the bit works independently of the other. That a broken curb bit does not necessaily mean you neck rein..?? BUT, on trail I do ride with slack in the reins. On barrels rightly or wrongly, I keep contact, which is why I think that it is a problem for Harley. He doesn't "like" that, but he does need help rating down for the turns. He's not lazy about running, and he will blow by the barrel with the snaffle, and tends to bend just his neck rather then his whole body.
I don't know if I'm describing this well enough:). My biggest problem is putting all the moves together at the right times.
You start rating them about 2 horse lengths from the barrel to get them time to get their butt's gathered up under them for the turns. When you get to the point to start the turn , slide inside hand down the rein, drop the outside rein grab the horn and push back, pull to your pocket, hold them in the turn with your outside leg, keep them off the barrel with you inside leg. about 1/3 of the way around the barrel your looking at the next barrel, 3/4 of the way around, your picking the outside rein back up to get them to move over to get ready for the next barrel about 1/2 to the next barrel you using your legs to get them in postion for the next turn.....to much to think about to remember to not pull too hard, but hard enough:) I just feel there might be bits that would work better then what I have, I just hate buying them and they not be right.
Becky