If you are set up to reload and don't mind working with wildcat or proprietary cartridges, you might look into the .30 Gibbs. It's basically a .30-06 case that blown out and lengthened a bit........a little more improved than an Ackley Improved and with a slightly shorter neck.
The beauty is that like the Ackley, the Gibbs can be fire formed from .30-06 just by seating the bullet a little long or you can purchase .30 Gibbs headstamped and formed brass by Quality Cartridge from Buffalo Arms and not waste the powder and lead for fire formng.
Herman Cain '12
Squished bugs on a windshield is proof the slow/heavy bullet theory works.