Sale, Transfer, and Storage of Firearms; Requires background checks on persons involved in firearm sales or transfers; requires firearm sales or transfers to be conducted through licensed dealer; revises requirements for safe storage of firearms; revises criminal penalties; requires firearms be sold by dealers with trigger locks or gun cases; revises warnings to be posted in gun dealerships; requires certain materials to be given to gun purchasers; prohibits specified acts involving unfinished firearm frames or receivers; prohibits certain activities involving three-dimensional printer or CNC milling machine.