I am puzzled that anybody would give these books mixed reviews. Really.
I have found that every Collector Grade Publication book I have bought was excellent. No less. They are well worth the money.
I have both Black Rifle books and I don't think you can possibly find any better references on the development, history, variations of the design, etc. There are chapters that also address the stupid in-fighting between the ignorant narcissist Sec. Def. McNamara and the Army, Air Force, and especially, the dunderhead Chief of Ordnance. The row over the forward assist mechanism that the Army insisted on, the Air Force thought was not needed (apparently, history has proved the Air Force was right, IMHO). The fiasco with changing from extruded powder to ball powder, the problems mfg. huge lots of powder that kept within specs., the results of the ammo trials among Winchester, Remington, and Federal Cartridge.
The first book, along with the historical overview, starting with Eugene Stoner (Semper Fi, Gene!) and his AR-10, early development, the SCHV trials, the NATO trials for a new battle rifle cartridge, etc. etc. It's truly an eye opener, co written by the publisher, R. Blake Stevens and Dr. Edw. Ezell (deceased). Dr. Ezell's name on the book alone should allay any fears this book is frivilous.
The second book, by Chris Bartocci, takes up the story with the development of the M-16A2, different 3 and 4 rd. burst systems, the M-4 and SopMod models, experimental models and features and has a very good addendum in the back showing all military model M-16 variants (including foreign licensees) and features and all the Colt civilian models and features up until the mid 1990s. If you are looking for a "picture book" with beautiful color pictures, none of the Collector's Grade Publication books are for you. There are plenty of b&w pictures, patent reproductions, production documents, copies of DOD and armed services memos, etc. These are historical books, not really coffee table books.
All the other books from this company are great, too. Check out Collector Grade Publications on the internet and read the titles. There's something there for most serious firearms enthusiasts. Most of the truly historical arms of the 20th century are covered by authors, and some by the publisher, Stevens. I think he wrote the books on the FN P-35.
Unless you are reduced to eating Ramen Noodles daily, good God, man; put down your money and buy these books!