The argument that a firearm that kills or injures someone when used correctly is a defective product is a difficult one to make because, well, that's what it was designed to do. However, if a poorly-designed or -built firearm blows up in the user's hand, then that would probably be considered defective, and the injured person might well prevail on a defective-product liability claim.

you are being extremely misleading and agendaed here. Either you have been brainwashed by propaganda, or you are intentionally doing it.

You cannot sue Mercedes if someone decides to use a car they manufactured to ram into people on the sidewalk. Well, Maybe you can sue, but you can absolutely not win.

On the same line of logic, you absolutely can not sue Walmart if your relative gets stabbed by a knife they sold, Had manufactured, or similar.

And then along the same line of logic, you cannot sue a gun manufacturer/dealer if someone decides to use a gun they sold/manufactured to harm someone.

Guns dont kill, people kill.

IF however a gun manufacturer ran advertising suggesting people buy their guns to shoot up farmers markets, schools etc. Or if gun sellers ran advertising with subliminal messages urging people to whack their neighbor, well then you absolutely CAN sue them, and would probably have a good case.

More similarly to this case here, IF a gun manufacturer made a gun that is obviously defective, leading to injury/death, and you had a leaker come and show evidence they knew about it, and didnt care, well then you would probably have a good case aswell.