Sorry for the confusion! Yes, by O-ring I ment loose ring, down here that's what everyone calls them, or just general "snaffle" means one aswell. Basically what Sorrelhorse posted, but without the fancy colors. :) (Though I do admit I like them too!)
By O-ring snaffle, do you mean an eggbutt snaffle? That is a good and a standard starting bit for a young horse. In recent years many people put a leather curb strap on a snaffle like this so that the bit won't slip through their mouths when you train. I wouldn't suggest a hackamore. You are the victim of people who think you're hurting a horse's mouth with any kind of bit, so the horse will respond and like you better if you don't use one. A mechanical hackamore will rub the hide of a horse's face if he's green and throws his head around.
You need either a trainer or you need to buy some NH methods so you know what you're doing. The best way to train is hours and hours of ground training for obedience. Since he's been backed, you could back him for about 5 minutes at the end of each session, but I'd go back and teach him to give to the bit ON THE GROUND, until he's soft and responsive.
Training horses isn't rocket science, and I'm sure you could get the job done, but I wouldn't use a mechanical hackamore on a horse that wasn't finished, IMHO.
I think you've misunderstood me on a few things. I did not try him in a hackamore because I believe bits are harsh, I just knew he was responsive to nose pressure on the ground, so I suggested to my sister (my equivalent to a trainer, she trains horses for a living) that we try one just to see how responsive he would be, which he responded tons better to.
I'll probably try backing after each session, like you suggested, and working with him in the snaffle on the ground aswell. I still may try the sidepull (Not a mechanical hackamore) for him to get used to my leg pressure in the saddle, as I imagine that would make it easier if I try to ride him in the snaffle someday.
A sidepull is the equivelent of a snaffle bit in bitless riding. My colt likes one, but I recently switched him to a twisted Myler snaffle (I do NOT suggest doing this with your colt. Mine has had a lot of training on him and is past his baby years.) so I don't use it on him anymore.
What are you looking to do with this colt? Might it be barrel racing (Guessing on your name here) I would suggest possible letting him go in a sidepull, then advancing your way up to a little S hackamore. Some horses just do better without a bit.
All around horse is what I'm thinking for him, if he takes to barrels, he may someday replace my gelding. I do think I'll try a sidepull on him, though. Do you think this would work? Mustang Nylon Side Pull - Horse.com