Imagine an ES plot line in which a group of powerful mages were striped of their ability to use magika because they're criminally insane.(why do they need to be criminally insane?) Still being insane intellectuals(point me to a criminally insane intellectual, please), they escape prison and go to Black Marsh (Black Marsh would be the last place I would go to mine for sulfur, charcoal, and potassium nitrate, which you need for gunpowder. Though I suppose you could 'summon' it...) where they begin development on the next best thing from destruction magic: Gun Powder.(wouldn't alchemy make more sense? In Oblivion alchemy dealt mostly with plants, but in the real world it dealt with primarily earth metals with plants being second hand) They make a deal with most of the local Argonian (tribes?) that for their service (gathering materials, production labor, dry storage and transport of said black powder), they would be armed with primitive firearms to take on slaving parties from Morrowind. When production is stepped up to full swing, Morrowind is invaded by musket toting Argonian guerrillas. The player would come into this somewhere, in the middle of a magic vs. technology conflict with all of Black Marsh and Morrowind as a map. (meh, magic versus technology shouldn't be done in my opinion and wouldn't be done if it were an option. I'd suspect everyone to use a combination if they could.
My point is, however unlikely that it will happen, Bethesda could think of something really cool to do with the idea of gunpowder in Tamriel.
Yes, but what army in Tamriel, magika or no, could easily defeat a force armed with rifles? Plate armored charges would only result in death, especially if the fight is taken to Black Marsh and Morrowind.
Hmm. I'm pretty sure a group armed with rifles would be able to defeat most enemies as long as they a) were well-disciplined and lead by competent commanders b)weren't heavily outnumbered c)weren't surprised and d)weren't fighting mages. Magic has so many advantages, even over rifles. I remember being part of a discussion of what outcome a war between Wizards versus Muggles (in the HP universe) would lead to. There were some people who went on and on about guns being faster than wands, being more accurate, etc etc. But then someone mentioned that a simple impervius charm, cast upon oneself, would repel all bullets. And hence, in the absence of a surprise attack, guns were rendered useless. And, I'm afraid, that's mankind's main weapon.
Keep in mind that a large force of British soldiers, at the turn of the twentieth century, armed with the best rifles of the day, were overrun by a large Zulu force that had surprised them---a force whose main weapons were short spears, throwing spears, and a a few older gun models---at Isandlwana.
Either way, the Elder Scrolls wouldn't have rifles to begin with. Guns have been around for a long time, dating back to the 1300s in Europe (the so-called High Middle Ages) and in Asia dated back even further, to the 1100s. Gunpowder itself had been known about even before then. And despite such a long history of guns, rifles only really began being used in the 1800s. So if Tamriel were to get guns in the next 200 years (assuming that's when Tes V begins) they would be far, far, far away from having a rifle. If anything, they'd probably have a hand canon. http://en.wikipedia.org/wiki/Hand_cannon .
And, I think it is worth noting, that even by the time guns largely replaced crossbows and longbows in Europe (1500s), crossbows and longbows remained largely much more effective than guns. Why were they adopted, then, you ask? Well, that is another discussion entirely, but lets just say they were adopted for reasons other range, accuracy, and piercing power (all of which bows were better at and remained better at for some time even after the adoption of firearms..).