Most large bases have a recreational range set up. Not all allow civilian access but, there is usually some form of of this through the MWR. (same organization that usually has canoe rentals, maintains the rec centers, handles hunting on the reservation and organizes family picnics/events, etc.)
From what I remember of Indiantown Gap, it isn't really a 'large' active duty post so I'm not surprised they don't have this type of facility set up. I seem to remember that Ft Drum does have this type of facility though.
Also, its not any range and we can't do full-auto. It is a specific range set up for recreational shooting. We get the benefit of very low cost, a nice and well maintained range and we can support the actviities center for base families at the same time.
There is another thread in here with details on the range. If you check out www.dix.army.mil you may find links or info about this type of facility at other installations.