In my wandering around the web seeking enlightenment toward a good balance between ammunition, rifle & marksperson (of which only the first two are variable, I’m stuck with the third I’m afraid) I stumbled across the; ‘History and Basic Design of the .223 and 5.56 ammunition’. It is a lightly written, very through, 53 page pdf download about more than you every thought to ask: http://ammo.ar15.com/project/AmmoOracle_061808.pdf It goes into purpose, choices, barrels, effects, legal and other issues. It might take a short while to down load. If you just want to bookmark the website, here is the link to the first page: http://ammo.ar15.com/ammo/project/hist_hist.html There are different ‘Chapters’ listed on the left side column. It is very well done and credit should go to Troy Tiscareno, Tatjana von E & Derek F. I’m posting it here instead of ‘Ammunition’ because it refers mostly to use in AR 15s. Maybe it should be stickied?