Michael Petrov nailed it. The Gerald Hammond series deals with adventures of two different protagonists, both Brits, one a gunsmith, gundealer, antiquarian firearms expert; and the other former military invalided out and dog trainer. Regrettably, he has stopped writing on either series.
An amusing series is by Nevada Barr. She details the adventures of a woman Fish and Wildlife Services warden. Also found in paperback.
Both of these can be bought used and reasonably cheaply on
http://www.bookfinder.com, just pay attention to the shipping charges.
Regards
