If you want a cold war era spy novel which is fairly realistic about firearms I suggest you look at Donald Hamilton's Matt Helm series. Not to be confused with the Dean Martin movies of the same name.
I don't always agree with the author's firearms opinions. (He thinks the .38 Special is a tremendously powerful round, for instance).
Still, he knows his stuff. There is also sex, common grade booze, but not much gambling.
He carried the series a little too far, but the early books are really good. The first one, Death of a Citizen, is great.