Lee, Look at the action screw first, if I am not mistaken, shooting loose is usually a problem when the screw is bottomed out on the barrel. Usually all it takes is filing or grinding a couple of threads off to shorten it slightly. You may also want to apply a little Guntite, or purple Locktite to the screw to hold it in place. In a pinch if you are a fisherman, and considdering the size of the screw, try insering a short piece of 4LB test line in ahead of the screw before you tighten it, it will hold it till you wish to loosen it again.
The strange part is what you said about your action being pulled in the center, dont torque it so hard you strip the threads in the aluminum receiver.
If you wish to make a solid "bedding" for the front of the receiver, cut a piece of aluminum that will fit in the inletted part of the stock where your action screw comes through, with a hole drilled for the screw. You may need 10 guage as loose as yours sounds, this will give you a solid bedding point though and keep the action from being pulled into the wood. This is very similar to what Volquartsen sells for a bedding kit. They go a little further with a stepped washer that fits around the action screw. And like the Volquartsen kit, you should probably put a piece of high density foam or rubber material at the front of the forearm, about an inch from the tip, in the barrel channel. This gives your barrel a presure point, and most find this with the bedding gives increased accuracy. You may want to experiment with the foam thickness, say 1/8" to 1/4" before compressing, and even how much you torque your action screw.
Oh yeah look at
http://www.weaponkraft.itgo.com/ for a neat little stainless action screw and the best bolt buffer on the market, or get the Preformance Package, you will not be sorry.
Hope this helps, Andy