Try a really soft bit (trust inno sense flexisoft d ring) to help with discomfort. Train with it! You said he's from slaughter and don't know his past, he may have a bad experience of was started rough. Start over, retrain him with the bit as if he's never carried one in his mouth. Ride in a halter, how does he behave? Is he the same? is he better? is he worse? He may prefer a bitless option. I love bitless but do not recommend hackamores. A horse's nose is very sensitive and hackamores (even fleece ones) are too hard due to the shanks which create leverage.
Hope this helps,
I gave my horse a treat or grain after everytime she took it. I slowly weaned her off the treats and now I just pet her but she practically opens her mouth when she sees the bit lol!
Think about it - you are putting a cold, metal, heavy bar into a horses mouth, which is a very sensitive part of the horse's face. Of course he hates it. No horse likes a bit. Some are more accepting and tolerant of them, but many are not.
If your horse throws his head, this is a sign of discomfort and that the bit is too heavy in his mouth. Depending on what bit you have it could be pinching his lips and could be putting too much pressure on his gums, causing him to toss his head and react.
Like Aries says, try a hackamore or a bitless bridle. Horses who are not accepting of the bit are more likely to prefer to receive pressure on their face rather than in their mouth. You'll find going bitless is a lot more cheaper, since it saves you having to buy a ton of bits to buy and try.
I ride my mare with a mechanical hackamore and she works wonders in it. It's great not having to fight her to get a bit into her mouth when tacking up and I honestly wish I had began her education bitless rather than wasting months trying and buying different bits.
Trust me. Try bitless and you'll see a changed, more happy horse to ride :)
Bit spray and or wipes you can also use a treat and put it above the bit
He doesn't take the bit, throws his head, and if you pull back on the reins he bucks. His teeth have been checked and he's from slaughter so we don't know much from his past. Just hoping to get him used to bits.
Try a hackamore. It is essentially a bitless bridle
How does he show that he "hates" his bit?