"shooting illustrated presents: The American Rifleman Guide To Black Rifles". I don't know if they offer it any more but I frequently use some old copies I have laying around as a resource and are hands down the best resources for ar info. Go to your local bookstore, i.e. Barns & Knoble, Hastings, etc. Some of the larger chains magazine sections have some great reading from sources you've never heard of. Also, gun tests is a great publication. Not just for ar platforms but tons of expert knowledge from unsponsered writers that have no obligation to stretch the truth. Guns n ammo was my mag of choicce until I found this gem. Gun Tests the consumer resource for the serious shooter.