Given your potentially variable yardage, I'd recommend a mid-weight bullet that'll open up at your max range. I'd take a look at "regular" (non-premium) bullets in the 150-165 grain range. Consider bullets like the Nosler hunting Ballistic Tips or Partitions, Honady SSTs, Sierra Game Kings, Remington CoreLocts, etc. I've had pretty decent results with factory Winchester and Federal ammo with basic 150 grain soft points. If you believe you need something a little more robust, consider Nosler Accubonds, Hornady Interbonds, or other bonded bullets. These have solid reputations for good performance near and far.