The Piltovan gunsmith Theory.
As we recall from the Burning Tides event, Graves had lost his one of a kind shotgun. However, he shrugged it off mentioning that he knew a piltovan gunsmith. Recently we had some interesting development with the Urgot rework, SHOTGUN KNEES! "Urgot isn't a gunsmith you idiot, awful theory!" No, what's interesting about Urgot, is the description of those shotgun knees "Attacking in the direction of one of Urgot’s legs causes that leg to combust flames outward", this is how Riot described Urgot's shotgun, I'm going to go out of my way to assume that Graves' would be described to work in a similar fashion (obviously the source of combustion being the reaction of the gunpowder and not necessarily intending that Graves' gun is shooting out flames). There is one person from Piltover that we know of, that it would make sense if they specialized in such inventions/ creations... Ziggs. It would be a major leap, from what he currently is, but what he currently does, (imo) doesn't fit in with the new Piltover. The old lore didn't even really expand, on what he did as the Dean of demolition, so it is difficult to say, how cemented Ziggs' 'plot-hook' is. The last I recall, a rioter mentioned Hiemer has a workshop in Piltover, and it sort of one of those places, where no one knows who works there, but its always been there and just sort of blends in. I'm not sure whether or not they confirmed that Ziggs works with Heimer, but assuming he does, that sounds like the perfect place, to get a one of a kind, magical shotgun, to me. We could even go as far as to assume that Ziggs could have invented/ (introduced to Runeterra) ballistics on a whole with this theory, as we know yordles live for what would be centuries (based on Poppy's and Kled's lores). A master of ballistics and master gunsmith, no doubt a shot gun made by him would be anything less than legendary. Also, it would be a neat way to introduce Graves and TF to other characters, that you wouldn't expect them to run into (whereas, its a guarantee they'll bump into Vi and Caitlyn), then that begs the question, would Graves know Ziggs is a Yordle? It would be funny if TF saw through Ziggs' 'glamour' while Graves is unable too. TF: "Your gunsmith is a rat??" Graves: " He's a hairy old man, but calling him a rat is going too far bud... You're the only rat here." TF: !!
As of now, Piltover has very little need for weaponry such as bombs (should Noxus invade. In the future, this would change) so why his he in Piltover making bombs? I have no doubt that the lore team would be able to answer this question once they sit down to discuss Ziggs' new lore, however, I hope if any Rioter happens stumble on this post, they take it into consideration whenever Ziggs' lore will be discussed in the future. I don't even play Ziggs, but I think this would make for an interesting new lore, I'd like your feedback on this theory, whether or not you support it. ^_^