Well, all five volumes of Chinn total nearly 3,000 pages, compared with just under 300 pages for Rapid Fire, and 350 pages for Flying Guns WW2 (the other two FG volumes total 400 pages, so that's 750 overall). So you would expect far more technical detail in Chinn. Furthermore, my books are as much about installations and use (especially in FG) as they are about the guns themselves - Chinn is weakest of all in this respect, saying little about installations, and that often wrong. There is also a lot more about ammunition in my books - a critical aspect of gun performance, but often ignored.
Chinn is actually the only source I know of for the technical detail of many of the guns he describes, but there would be no point in just copying all that - even if I could make the space available.
Comparative evaluations of different weapons, in terms of their performance and reliability, are extremely hard to come by. One of the few examples I know of concerns the WW2 20mm Hispano vs the .50" Browning aircraft guns (the Browning was three times better, at one failure every 4,500 rounds cf 1,500 for the Hispano). That's about it...
If you want detail on Russian guns then the go-to book, without any doubt, is Chris Koll's "Soviet Cannon" which deals in great detail with all Soviet automatic weapons and their ammunition, from 12.7 mm to 57 mm. It is the final word on that subject, and is absolutely superb.
I don't know about availability of the Davis book - I have only seen photocopies.
