I've long enjoyed reading Donald Hamilton and Jonathan Gash, and look forward to reading Gerald Hammond.
A few others that may prove to be of interest:
Single-Handed, published in the US as Brown On Resolution, by C.S.Forester of Horation Hornblower fame. Forester also wrote Rifleman Dodd and The Gun, about the Napoleonic period.
Almost anything by Wilbur Smith, all are about Africa. Not much specifically about guns but it's obvious he knows his stuff.
Again, almost anything by Stephen Hunter whose main character is a skilled sniper named Bob Lee Swagger, these are fairly fanciful but just barely believable
A few stories by Guy Lautard who wrote The Machinist's Bedside Reader series, most are included in his machining tips books and one of them describes how to fabricate and operate a color-case-hardening setup. BTW I highly recommend these machining tips books for anyone interested in gunsmithing.
Of course all of the J.M.Pyne stories reprinted (I believe) by the editor of The Single Shot Exchange magazine, about a thinly-disguised Harry Pope.
Patrick O'Brian's series about the Aubrey-Maturin voyages of the Napoleonic period. Again not a lot about small arms (as opposed to cannons, there's plenty about cannons!) but again it's obvious he knows his stuff. There are almost 2 dozen of these and I found each one to be totally engrossing.
Reading is good clean fun and will keep you and your kids off the streets and out of trouble.
Regards, Joe