Specifically in Colorado? I will have to think about that awhile.
OK. I strongly suspect the same ammunition that is best in New Mexico, Utah, Wyoming and Montana will probably work just as well in Colorado.
My preference would be a hard, cast bullet over jacketed as the extra velocity and lack of expansion will contribute to deeper and straighter penetration. The Federal 180 Cast-Cor would be my second choice, after my own handloads. First choice, if limited to factory ammunition, would be this Federal load. And it wouldn't be out of a 3" barrel if I had a choice, it gives up too much velocity!