From NRA-ILA:

Congress, through the Protection of Lawful Commerce in Arms Act … has broadly prohibited lawsuits “against manufacturers, distributors, dealers, and importers of firearms … for the harm solely caused by the criminal or unlawful use of firearm products … by others when the produced functioned as designed and intended.” … The present case seeks damages for harms … that were caused solely by the criminal misuse of a weapon by [the perpetrator of the Newtown slayings]. Accordingly, this action falls squarely within the broad immunity provided by the PLCAA.