> But if instead Walmart were selling guns preloaded without warning the customers that there were bullets already in the guns, I would argue that Walmart would be at least some percentage at fault when some percentage of their customers inevitably shot themselves or others

I see your point, but I think it might be worth clarifying that despite Walmart's probable liability, this would in no way indemnify their customers; the first rule of gun safety is RESPECT EVERY GUN AS LOADED until disassembled into its component parts, no exceptions.