I always thought it would be cool to have some sort of primitive musket in this kind of RPG. Kind of like the Airship in Icewind Dale. Crazy Inventor, Crazy Invention.
It could be slow loading, kinda scary once it gets going. There could just be one in the world, so a quest would have to be involved.
I just don't have the knowledge or the means to do that kind of thing myself.
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I had a rifle download for Morrowind towards the end - used the crossbow action and the bullets came from the arrow aimation - so I guess you could make a musket in Oblivion.

Thing is, Oblivion doesn't have crossbows. I suppose you could make a staff like this, though. I think the blasters in the Star Wars mod were modded staffs..

I have seen one that was a rifel but have searched google for about a half an hour and cant find it. (you might want to check planet elderscrolls b/c i think thats where i found it) i didn't download it because its pretty useless and uses welkynd stones as ammo (they too valueable to waste like that).

On tessource there is a mod called blunderbuss i think you should try it