Perhaps it goes back to Tolkien when he said* in The Hobbit:
More recently there was the novel Grunts by Mary Gentle, and Warhammer 40,000 has the Orks, which gave us the meme of Dakka. Any other entries worth looking at?
*they were called “goblins” in The Hobbit, but that’s pretty much accepted as beta-Orcs.
Not a book, but Bakshi’s movie “Wizards” could arguably fall into this. I haven’t actually SEEN it, but I’m under the impression it involves goblin-y characters with guns.
I’ve seen it. They’re not explicitly “orcs”; the in-story term for them is “mutants”. But they sure look like them.
Still, though, machine guns and the like were the least of their weapons. The most potent weapon the forces of evil wield in that movie is propaganda. The evil wizard uncovers some millenia-old Nazi films, and through a combination of technology and dark magic, is able to spread the spirit of those movies over the battlefield, spurring on his own troops and demoralizing their fairy opponents.
Perhaps this genre isn’t as widespread as I thought. I may have been conflating Grunts with the Orcs series of novels by Stan Nicholls, which upon review is Orc-centric but AFAIK sticks to pre-industrial weapons. Or in turn conflating both with the Orks.
I’m not sure how much they focus on Orcs with guns things, but there was a serious of novels based in the ‘Shadowrun’ universe.
Shadowrun was a cyperpunk setting where magic had returned to the world, so you have fantasy races (including orcs) running around in a near future world.
You might find some of what you are looking for in some of those novels.