This is like a mini-version of M.D.C. Crawford's 1938 The Influence of Invention on Civilization, except author Chris Kyle confines himself to the evolution of a single invention- the gun; and he confines the historical range to the history of the United States. It's not a high-brow academic work, but a decent pop-history by a pretty knowledgeable author- Kyle was a former Navy SEAL, and you may have heard his name before, both because he was the inspiration for the film "American Sniper", and because his mysterious death has raised questions about whether he may have been a CIA operative who was in turn terminated by the organization.
All that aside (because it really has nothing to do with the book), there are some interesting insights to be found in here.
The American long rifle: Proved superior to British infantry rifles in the American Revolutionary War, because the American gun had a rifled (i.e. ridged) barrel, imparting a spin on the projectile, increasing both range and accuracy. Kyle explains how this was well suited to the sniper-heavy guerilla tactics the Americans used in that conflict. The rifling didn't win the war for America, but definitely helped them make the most of their small forces- enough to hold on long enough for France to enter the war and tip the balance in the colonists' favor.
The Spencer Repeater: One of the first multi-shot rifles. In armed conflict, the "repeater" allowed soldiers to shoot multiple shots before needing to reload. Pretty easy to see why this was an advantage, and sure enough: it was a major factor in the North winning the American Civil War.
The Winchester 1873 rifle: Excellent discussion in this part about how the Indian Wars of the 1860's- 1880's were mainly fought on the flat, wide-open Great Plains, where there was little cover, and success in armed conflict depended on powerful guns with a longer range than one's opponents, and the requisite accuracy to actually hit one's target.
The Thompson submachine gun (TSMG): Taking the advantage of the Spencer Repeater to its logical conclusion, if automatic weapons are good, fully automatic weapons are even better! TSMG was developed for World War 1, but the war ended before it saw much use. Notoriously, it was Prohibition-Era gangsters like Al Capone, "Babyface" Nelson, and "Machine Gun Kelly" completely outgunning legal authorities which demonstrated the utility of this weapon. It also proved useful in jungle conflict in World War 2 (Guadalcanal), where extremely limited visibility makes the ability to "spray lead" over an entire target field decidedly advantageous.
The .38 police revolver: A bit counter-intuitive, because most of the evolution of guns follows the chase to deliver more and more firepower. In the case of the .38, however, the weapon's beauty is in delivering less. Police guns seek to strike a balance between matching the current firepower of outlaws, while avoiding munitions so destructive they pose a reckless threat to bystanders. Police officers (ideally) want to stop criminals who pose a direct threat, but don't want to go shooting rounds so powerful they are likely to pass through walls and still be lethal to unsuspecting families in the apartment next door. Law enforcement ideally results in live capture and trial of a criminal, not inevitable death every time a gun needs be fired. Also, police work frequently involves a lot of running about, so it helps if the gun can be not only serviceable, but lightweight. The .38 apparently strikes a nice balance of all these features, as it has been the most popular gun for American police forces for going on 60 years.
These summaries are very minimalistic- Kyle fills them out deftly. In all, he covers 10 guns, and brings the reader from the American Revolution to our present-day conflict in Afghanistan, where he speaks from experience, because he served there. There are a few areas in the text where his explanations got a bit over-technical for me, describing the inner mechanisms and components of the more complex firearms, but overall I found it to be very dilettante-friendly, which is where I'm at on this subject.
3.5 stars because it is a little flat in areas, and because there are several rifles, which- although probably worthy of discussion, sound too much like the rifle just discussed in the previous chapter, except a little bigger/better/more accurate. I read it in two days, and I'm not a fast reader, so it's definitely worth the time investment, if you're interested in military history.