Gun Mfr suits and the dormant Commerce Clause
It seems as if at least some of the (now dying off) suits against gun manufacturers would face a serious problem under the dormant Commerce Clause. Specifically, the suits which allege that a manufacturer should be liable because they sold guns to State A, where they are legal, and should have known that some would flow from there to State B, where they are more strictly controlled.
The Commerce Clause empowers Congress to regulate interstate commerce; the dormant clause application of that forbids States (at least beyond a minimal level) to interfere with interstate commerce. (The dormant clause comes in with some frequency, as States try to forbid shipment of this or that through their borders, or impose special regulations on trains or trucks passing thru the State, or try to tax trucks and other equipment used in multiple States). In the above setting, State B (or its courts) is clearly being asked to interfere with legal commerce to State A.
As a thought experiment, let's flip the setting around. State A is the place of business of a gun manufacturer, and it enacts a law imposing a civil penalty of $100,000 plus attorney fees for filing of a lawsuit (anywhere) seeking to impose liability on a manufacturer within its borders, for a lawful gun transfer. Or its courts evolve a comparable doctrine: such a suit is an abuse of process, rendering plaintiff liable for actual and punitive damages.