I don't really find that too hard to believe actually. But that may be my familiarity with fire-arms. (I own over 70 weapons. From revolvers all the way to assault rifles).
You have to remember, all a gun is, is a bomb with a directed discharge.... which is why high quality steel is used in the construction of the barrel, breech, and lock.... changing out the tensile strength of the steel for ceramics/plasteel means making sure the materials can withstand multiple factors... some things to worry about:
Heat
Expansion
Pressure
Durability
Weight.
As I said a gun is essentially a directed explosive bomb... you have an amount of explosive peopellant that is ignited and either pushes the bullet down the barrel, or causes a rapid expansion of the breech. (IE: BLOWS UP IN YOU HAND!! - yes i have had this happen!)
There is a careful balance here that gunsmiths have to worry about....
Because this is a directed explosion, you have heat, extreme amounts of it... which steel has some advantages with... one: steel heats up and disapates heat rather quickly, which - along with its tensile strength, means that the weapon is not (if made right, and used right) is not going to warp, deform or melt.
Steel is also durable. Properly forged steel won't crack, chip, splinter, or bend easily, which means steel can be subjected to all sorts of ohysical environments and handling without much worry of failure. A steel barrel can also withstand the forces and friction generated by the bullet, and affect it! (Barrell rifleling puts a spin to the bullet, decreasing wind friction, increasing accuracy and range).
Ceramics have a few qualities that are helpful - at first glance.
Its an insolator, so it handles heat extremely well. It does not have expansion characteristics (not going to deform). But ceramics are prone to cracking, splitting, and chipping. Ceramic tensile strength is also rather low...
So finding, forming, and molding ceramics into the parts needed, with the tensile strenght needed to handle repeated explosive force, and mechanical stress and shock would be one heck of a job. Especially without increasing the size, bulk and weight of the weapon.
To date, there is NO entirely ceramic firearms that have ever been made. The closest we have gotten is David Byron and Magnum Technologies. In 2000 they accepted $800,000usd to make a "airport proof" (entirely non-metal) sidearm for the US government. Magnium Technologies closed its doors in 2007 without even presenting a prototype.
