Murder in the Gunroom by H. Beam Piper, Fiction, Mystery & Detective

Gladys Fleming had her doubts. Enough at any rate to engage Colonel Jefferson Davis Rand--better known just as Jeff--private detective and a pistol-collector himself, to catalogue, appraise, and negotiate the sale of her late husband's collection.
There were a number of people who had wanted the collection. The question was: had anyone wanted it badly enough to kill Fleming? And if so, how had he done it? Here is a mystery, told against the fascinating background of old guns and gun-collecting, which is rapid-fire without being hysterical, exciting without losing its contact with reason, and which introduces a personable and intelligent new private detective. It is a story that will keep your nerves on a hair trigger even if you don't know the difference between a cased pair of Paterson .34's and a Texas .40 with a ramming-lever.
"Well, have you thought that it might just be suicide?" Kathie asked. "I have, briefly; I dismissed the thought, almost at once," Rand told her. "One, that if it had been suicide, Mrs. Fleming wouldn't want it poked into and two, I doubt if a man who prided himself on his gun-knowledge would want his self-shooting to be taken for an accident."