From what I am reading, your limited to what you can use. Something about the projectile can not be twice as long as the caliber and no pellets. In that case have you considered LEE R.E.A.L. conicals. They are pure lead, 320 grains would still fall into that legal area for you. I realize that might be a little small, but the only other choice I would look into is the 405 grain powerbelt, if that is legal. I am not sure about the length of that powerbelt. Otherwise the 348 in a aero tip would be a good choice. What you want is good penetration and expansion.

The Lee Conicals would give you the penetration. If you put it in the right place, a half inch hole through the heart or lungs is going to ruin anyones day. They will expand but they have to hit bone usually. It would not hurt to get some and try them out, see how your rifle shoots them. Run a search on Black Jack Hill. He sells them very reasonable, and they shoot excellent in my in lines....