A good summary by historian Victor Davis Hanson of the major trends that culminated in the development of the assault rifle, generally, and the AK-47 specifically. There are some inaccuracies as to dates (such as lumping the Maxim machine gun together with the general development of weapons in the civil war; and dating the earliest assault rifles as post-WWII when, in fact, the Stg-44 was developed in the waning years of the war), and a few other points I disagree with, but a good overview nonetheless.
Hanson mentions two books in his article: The Gun, by C.J. Chiver, and AK47--The Weapon That Changed the Face of War by Larry Kahaner. I've read both books, and I would definitely recommend Chiver's book over Kahaner's. For one thing, Chiver's book appears to have been better researched inasmuch as Chiver draws upon Russian sources that Kahaner either didn't have available or didn't use. To be fair, Kahaner's book also has a slightly different perspective or purpose so that information from the Russian sources probably are not significant to his thesis.
That, however, leads to my second reason for recommending Chiver's book. Kahaner's book is an primarily an indictment of the international small arms trade, and hand-wringing about countless brush wars, and only secondarily about the AK. The AK is merely the author's whipping boy. Chiver's book, however, is about the AK, but inevitably drifts into the international arms trade because the AK dominates the international small arms markets. I disagree with both author's conclusion that the ready availability of AKs has fueled wars, but that is an issue for another time.
For the American perspective, and the development of the M-16, I would heartily recommend American Rifle, A Biography by Alexander Rose. It starts with the earliest American rifles at the time of the revolutionary war, but the bulk of the book pertains to the post-WWI developments and the sometimes opposing forces between slow, accurate, long-range fire, and fast, suppressive fire that ultimately result in the production of the M-16, and takes it up through recent experiences in Iraq.