I'm not certain, but I think steel.
Here is the description from the website for the Escort MP-P which I have and is pictured above:
"Escort also offers a tactical variation for home and office defense. The MP-P/A TacStock2 model comes in either pump or semi-automatic action. These defense-style shotguns offer the same high performance function and reliability as all other Escort models, with features that have been designed for tactical use. The stock has been designed with a vertical pistol grip for better control, and an extended slide forend with Picatinny rail to provide a solid grip and reliable function from a variety of shooting positions. The stock also has a built-in shell holder that carries two extra rounds. Pistol Grip has cushioned inserts. Sights have been designed for quick target acquisition, using a height adjustable fiber optic front sight in an elevated housing, and a ghost ring rear sight that is fully adjustable. Available in 12 gauge, cylinder bore, 18 inch chrome moly lined barrel chambered for 3 Inch magnum loads."