Gun Control & RKBA

According to Cornell
https://www.law.cornell.edu/wex/products_liability]

a Prima Facie Case (for the commercial seller of the defective product) requires that

The defendant sells a product that the plaintiff uses
The defendant is the commercial seller of such a product
The plaintiff suffers an injury
When the defendant sold the item, the item was defective
The defect was an actual and proximate cause of the plaintiff's injury

I don't see anywhere that there was an allegation that the bump stock was defective.

Utility is a defense used when the items is defective to show the defendant is not liable for a design defect if evidence shows that the product’s utility outweighs its inherent risk of harm.


https://www.google.com/patents/US8127658]

Here you have an item that has been around since at least 2009 with many tens of thousands (if not more) sold and here we are 8 years later with the first instance of criminal misuse (that I'm aware of). That would tend to show that the product is not unreasonably dangerous and was not foreseeable for injuries to others if it took this long to happen with so many of the items sold.