You should check out Parker Productions. The Hydra-con (50 Cal 440 gr) complies with Colorado's regulations. I geared up with some a few years ago expecting to draw a Muzzleloader Elk Tag. Going into this year I have 21 pts and will most likey never have enough to draw the tag I would like. That is another story. These bore size rounds are used with "food grade" grease and a felt pad. They group well with my Knight Wolverine and I have taken two Antelope with them. Parker also has saboted bullets that work extremely well where legal. I have killed Antelope at 190 and 220 yards with the 250 gr Jacketed Hydra-con. The 250 gr Jacked Ballistic extreme is also a great round.