This is a Magpul Industries Stock known as the Hunter X-22 Takedown, model MAG760-GRY.
The Magpul Hunter X-22 Takedown chassis is an ergonomic" full-featured stock specifically designed for the Ruger 10/22 Takedown series of rifles. Made from high quality reinforced polymer" the Hunter X-22 Takedown features an ergonomic grip" adjustable length of pull and comb height to fit a wide variety of shooters" multiple sling mounting options" a non-slip rubber butt-pad" and M-LOK(R) slots for accessory attachment. The Hunter X-22 Takedown fits standard Ruger 10/22 Takedown .22 LR pattern rifles with no gunsmithing" and a reversible barrel tray ensures proper fit with factory pencil profile as well as heavy bull barrels. Made in U.S.A.
Features:
Compatible with all capacities of factory Ruger 10/22 magazines
compatible with all factory Ruger 10/22 Takedown .22 LR receivers
M-LOK slots