Roger Zelazny's Amber Chronicles had the gamut of modern technology, and why gunpowder didn't work when you got to Shadows closer to Amber (the physics was diff

Roger Zelazny's Amber Chronicles had the gamut of modern technology, and why gunpowder didn't work when you got to Shadows closer to Amber (the physics was different). There were guns, and tanks, and in one surprise battle, the protagonist devises gunpowder that does work in Amber and lands rifleman atop sword-and-sandals fighters to cause a huge upset. If author hasn't read Zelazney, then he doesn't know fantasy.