Like the title says, this is unofficial, but i found it very interesting. Talks about the many different things such as the height of space marines, the way a bolt from a bolt gun works, and stuff about the Eldar, Tau, and Human. Like i said, this is unofficial but it gives some insight into these things. http://www.philipsibbering.net/WH40KRP/WH40KRP_Concepts.htm I would talk more about it but i need to go to work so enjoy this find. :)
All this stuff may be unofficial but i found all this here to be quite interesting. About the bolter and space marines i thought he did a clever job there.