Looking for a story a lot like Gina Marie Wylie's "Tangent"--close enough that it is probably also inspired by H. Beam Piper's works. A man is transported back in time or to an alt. universe where he makes significant advances in military tech. Specifically I remember references to the round disks used for mortar propellant that were worn in belts (This is what disqualified "Tangent"). I could be completely mistaken, but I'm a big fan of this story type and would like to add it to my library if possible.
(Other "Tangent"-like story suggestions are also appreciated)