hmm.. not looking real good for you there P7cat. There are a few dept. of Cons. ranges around and a few private indoor ones but not much for just plinking. Sad to say it but your best bet is way out in warren country at Reifschneider. It is a ummanned Dept. of Cons. range and officially you can only shoot at paper and it has to be posted on the stands but, well, drop in there and you will see what I mean. Other than that there is always Mark Twain National forest. Target shooting is allowed and it is a huge place. just be damn sure of where you are and where everything else is before opening up. Contact the Potosi Ranger Dsitrict office for more info on this one.
Other than that read the post torward the top of the listings on the missouri hometown board listing ranges. Lots of good info there.
Good luck and have fun!
Oh, and be sure to come join us in one of our organized MoDCC/CMMG shoots, you can read about them on the board here quite often.