The outcome followed a seven-year legal fight with Remington Arms, the manufacturer of the Bushmaster semi-automatic rifle, which was used to murder 20 children and six adults in Newtown, Connecticut.

The attack was carried out by Adam Lanza, 20, who killed himself as police arrived on the scene. The children he killed were six and seven years old.

Families of nine of the victims brought a wrongful death case against Remington and its insurers in 2014, arguing the gunmaker should be held in part responsible for the shooting.

While a 2005 federal law protects many gun firms from such lawsuits, the plaintiffs were able to avail themselves of a Connecticut law that addresses deceptive marketing practices.

The families rejected a $33m settlement offer last year.

Joshua Koskoff, the attorney representing the families, said: “The immunity protecting the gun industry is not bulletproof. We hope they realise they have skin in the game, instead of blaming literally everybody else.”

The parents of one of the victims, Noah, said: “One moment we had this dazzling, energetic six-year-old little boy, and the next all we had left were echoes. However, the resolution provides a measure of accountability in an industry that has thus far operated with impunity. For this, we are grateful.”