In the november, 1964 issue of _Analog_, on sale in early October, there appeared a novelette by H. Beam Piper called "Gunpowder God." It was accompanied by a spectacular cover by John Schoenherr. Roughly a month later, because of personal and financial problems, Piper committed suicide with one of his guns. (He was an ardent gun collector, and his knowledge of guns was used extensively in his writing.) Almost exactly a year later, a sequel to "Gunpowder God" entitled "Down Styphon!" appeared in _Analog_, this time with a cover illustration by Kelly Freas.
The two novelettes were assembled into a paperback novel, _Lord Kalvan of Otherwhen_ (1965). It's a good novel, but I can't help but feel that it is a bit incomplete. There are enough loose ends hanging at the close of the work to make me suspect that a third novelette was planned but never written.
The Lord Kalvan stories were part of a larger series of stories that appeared over the years in _Astounding/Analog_ called the Paratime Patrol stories. They involved an undercover police force that patrols alternate history timelines to squash skulduggery among them. Most of these stories were told from the point of view of the Paratime cops. The Lord Kalvan stories are told mostly from the point of view of Calvin Morrison, a member of the Pennsylvania State Police who is accidently snatched from our own timeline into an alternate history in which America has been settled by the Aryan races who migrated east instead of west. He begins to rise rapidly in this timeline. But the Paratime cops fear that they may have to kill him.
In the anthology, _The Good Old Stuff_ (1998), Gardner Dozois argues that while _Lord Kalvan_ was not Piper's best book, it was "his most _entertaining_ book" (305). This is a fair assessment. It seems incredible that Piper could entertain at a time when he was wrestling with his personal demons, but he did. Give this book your attention.