I was out exploring Pawnee Grasslands yesterday and there is a huge area for shooting inside the park
. It was off of CR 65 and 69. Tons of people out there shooting anywhere from .22, AR-15's, clay pigeons and handguns. You can setup your own targets and lots of little berm areas. They are also setting up a new shooting area off of CR63 and CR96
Very fun place to drive offroad, see some wildflie, shoot and make a day of it. Took about 2 hours from Littleton to get up there via I-25 and going through Carr back towards the NW entrance.