Getting to 300 yards for deer sized game is fairly easy with a standard muzzleloader. Give it a good bedding job and find the right load. My .50 TC Omega will shoot 4" groups at 300 yards with a 300 gr SST in a black Harvester sabot, pushed by 85 gr by weight of BH209.
For long range elk, I need to up the speed, so I am building a RemPac 700ML. The Parker Productions Match Hunter bullets are the top dog for best BC and pushing them 2400 fps with large doses of BH209 will get me over 1500 lb-ft of energy at 500 yards.