So my mare has finally arrived!! She is so sweet and so smart. I am still learning about her but I am don't think she likes gag bits.. which is what most of my bit collection is made of. I have a select few fixed bits, including the derby lifter bit with a copper roller, and a Charmayne James grasshopper bit.. and I believe that's it. I have a Jim warner hack and a little S, but she does not like having pressure on her nose (the previous owner had a tie down on her, she does not need it). She will toss her head. 

I suspected her dislike for gags when I first tried her, as they did have a CJ chappy bit on her and she kept chomping on it, pushing her head down and trying to get away from it.. although she was still controllable. Please note she got a FULL exam by a very reputable vet before I bought her, checked her teeth and even her TMJ joint. Full xrays on hocks, ankles, stifles, and feet. The second time I rode her I put her in an L&W locked snaffle with a copper wrapped mouthpiece and a lifesaver..and she worked a lot better in it. Didn't fuss with it, she was still controllable but I didn't think it was quite enough for her when I worked her on the pattern. I don't think she is in pain anywhere. 

She is a finished barrel horse, and this is the first time I have purchased a finished barrel horse. She does need to learn to get her head down and collect, but I feel that will come with time because she gets a bit hyped up and ready to run when I ask her to lope. I have been working with her on that as I would like her to know she doesn't always have to run, just when I ask her to. I am worried about fussing with her too much because she IS finished, but I'm not sure what kind of bit I should try on her as I have mostly used gags for most of my horses. 

I would try the Grasshopper bit on her, and see how comfortable she gets with it after a few rides, I like how the chain mouth conforms to the mouth.. 

Could it be the copper or the type of mouth piece you are using moreso the the bit itself?  meaning, I have a horse that does NOT like copper mouth pieces, but loves the sweet iron... 

What do yours have?

I love the Jim Edwards line of bits. I slow work mine in the short shank ball correction, and sometimes I throw in the medium shank flat correctional. I wouldn't hesitate to run mine in the ball correction, I don't, but I wouldn't be afraid to. I find that sometimes those horses are nervous and chomp because they don't like the tongue pressure of "barrel bits" and will actually work better, be softer to the bit, when you relieve that pressure. I actually go back and forth and find I like the combination.