I personally adore the Peasant Railgun and other such silly tropes generated by player creativity! Lateral problem solving can be one of the most fun parts of the DnD experience. However, these shenanigans often rely on overly convoluted or twisted ways of interpreting the rules that often don't pass muster of RAW (Rules As Written) and certainly not RAI (Rules As Intended) -- despite vociferous arguments by motivated players.
Any DM who carefully scrutinizes these claims can usually find the seams where the joke unravels. The DnD authors also support DMs here when they say that DnD rules should not be interpreted as purely from a simulationist standpoint (whether physics, economy, or other) but exist to help the DM orchestrate and arbitrate combat and interactions.
In the case of the Peasant Railgun, here are a few threads that I would pull on: * The rules do not say that passed items retain their velocity when passed from creature to creature. The object would have the same velocity on the final "pass" as it did on the first one. * Throwing or firing a projectile does not count as it "falling". If an archer fires an arrow 100ft, the arrow does not gain 100ft of "falling damage".
Of course, if a DM does want to encourage and enable zany shenanigans then all the power to them!
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