No, but there ARE Carbon Fiber barrels for AR-15s out there.
While printers cannot AS YET extrude carbon fiber, I suspect they WILL be able to within a year or two.
Back ends, I suspect, will have to wait for home laser-sintering or E-beam sintering printers. . . but I expect those to be available in hobbyist designs within 5 years. . .
That was kind of what I was thinking (in re the sintering at least). 3D will work for the parts that have to be metal when 3D can (cheaply) do metal. So status quo ante from a detectability standpoint. The change is in far more widespread access to the tech, not any impact on detectability.
Carbon fiber barrels are thin steel barrels wrapped with carbon fiber. You will never be able to print them.
Carbon fiber wrapped barrels still have a steel bore.
It would not take much in the way of engineering know-how to fabricate a barrel out of steel bar-stock available at any machine ship.
A metal lathe, a drill press, a clamp and a micrometer are all easy to operate.
Being able to use a 3D printer to get the more involved bits would save some time.
The real issue as I see it is propellant. Making smokeless powder might be harder than making the weapon