3D Printing With Carbon Fiber Composite

Well, not quite.  But there is a 15% carbon fiber composite reinforced PLA now available for 3D printing.  The numbers that this article gives for "stiffness" do not make any sense for tensile strength, nor for Young's Modulus, but they do suggest that many gun parts that you would be reluctant to make out of ABS or PLA might make sense to make out of 4043D PLA + 15% Carbon Fiber.