To get there from I-25, exit #243, Highway 66 and go west. From within Longmont, just go north to Highway 66 (Ute Highway). From Boulder go north on Highway 36 to Highway 66. Great, now you're all on Highway 66 heading west.
In Lyons, the road will fork to the left (Allenspark) and to the right (Estes Park) just at the western edge of a small downtown. Follow Highway 7 north towards Allenspark. Drive for approx. 14 miles to the intersection of Highway 7 and Highway 72 (to Nederland). It is a pretty obvious intersection, so you can drive without worry of missing it.
The shooting spot is about 200 yards BACK from the intersection on Highway 7. We'll have a sign out pointing the way to the "range". It is just off the road and will be easy to find. Parking might be the only trick. Just across the road from the range is a former campground and scenic overlook that is marked Private Property. It looks abandoned and may be useable. If not, then just park on the side of the road since access to the range is blocked to vehicles.
See you there!