Have you played the Lifeline expansion? I rarely, if ever, used guns before I got Lifeline, but my experiences in Danforth have resulted in me always carrying one when scavenging.
I have lifeline but haven't played it yet but I always bring a fully loaded gun with me on any run though. I've had a few encounters where things went from bad to worse and a firearm is the only thing that kept me alive.
I really need to get back to playing this, I rage quit after an espescially bad session of Breakdown a few months ago and the taste of bile is still in my mouth whenever I think of starting over again. I will one of these days though, the missing achievements will haunt me otherwise.