While not about shooting, Project Guttenberg has thousands of free ebooks, in various formats.
http://www.gutenberg.org/
Or a quick link to the the top 100
http://www.gutenberg.org/browse/scores/top
The are free because they were written before 1922, and the copyrights have now expired -- they're all "Public Domain." Old doesn't necessarily mean bad. I'm reading the Sherlock Holmes downloaded off this site, because the ePUB format (with the
Mantano Reader Premium reader app for $6.99) looks better than any print version I can buy.
All kinds of formats are available, including plain old html, but I'd only use that if I were desperate.
I currently read on a Kindle Fire, and I find Kindle editions borderline unreadable. But the typography using the Mantano app is quite nice. I think I could make a nicer ebook using pdf format -- everything controlled by the typesetter -- but it would be close. My wife, who cares about style, uses an Apple iPAD, and I will allow they do a nice job as well.
Anyway, point of all this is there is a lot of reading that can be done for free, and there was good stuff written before 1922.