Why do we need to buy a Fizzco Bot Rifle from Two-Hat Jack when there's so many of them laying around? Because they're designed for robots, not humans. There probably had to be no shortage of modifications and ergonomics to account for before the player could actually use the thing, similar to the Charge Beam from Bomb Bots.
There's a pattern to what weapons are strong against each faction. The horde-based, unarmored and zombie-like OD are particularly susceptible to the wackier, more makeshift weapons like the Flaming Compensator or the High Fidelity. They get easily torn apart by whatever strange ammunition these guns happen to use. Scabs, who are mostly normal humans with normal capabilities and body armor, are more resistant to these makeshift weapons, but are easily put down by conventional guns like the Dirty Harry or the AK-FU. High-velocity records wouldn't cut through an armored human the same as an OD, but a bullet in a vital organ will drop them dead in a way that simply wouldn't work for an OD. Fizzco robots are sophisticated killing machines, and are very resistant to both of the above kinds of guns. However, they're vulnerable to high-tech weaponry designed specifically to subvert their hardware or software, like the Murderang or their own Fizzco Rifles. In addition to fitting logically, they fit thematically — the grotesque, fantastical orange-soda apocalypse monsters are weak to zany, slapshod apocalypse gear, the grounded, realistic humans are weak to real-ass goddamn guns, and the sleek, futuristic robots are weak to weaponry that matches their tech level.
