Mr Rawles,
I saw the letter you posted asking about the ballistic protection afforded by common building materials. I did some experimenting on this topic, testing the protection of concrete-filled blocks against a number of common calibers. You can see my findings here:
http://www.clairewolfe.com/wolfesblog/00001296.html [1] and here: http://www.clairewolfe.com/wolfesblog/00001404.html [2]
Even 8 inches of concrete offers only temporary protection from rifle ammunition (though it’s quite good against pistol fire.) For info on other materials, you might direct folks to: http://www.theboxotruth.com/ [3] – Ian