Per my measure - of the .504 bullets pictured below, any of the bullets including and to the left of the 500 grain N373 would be Colorado legal. Of those four, I would choose between the N373 or the NEx 460.
Cdad, yes - ah git $80 evertime sum1 orders 1000 wads frum TOTW an $150 evertime sum1 orders a bullet frum Dan.
Hmmm, kickbacks...