Bit info, I might be using wrong bit

Can anyone tell me about a Billy Allen bit? Are they considered harsh or gentle. I have a 16 year old quarter horse. Not sure what bit he was ridden in before myself. He has great ground manners, very nice boy, I can do anything to him, fly mask, fly spray, brushing, hanging on, loads, does alright in the arena, can walk him out of arena, not on him, he is fine, as soon as someone is one him he throws his head,becomes jumpy, but again not in the arena. He used to move cattle before I got him. My test ride was great,on a trail, had a trainer ride him, made several visits to make sure no drugs. I am thinking that maybe I an using wrong bit. Any suggestions? Thanks