This is a Magpul Industries Stock known as the MOE SL-S, model MAG653-FDE.
The storage-capable version of the flagship Magpul MOE SL(TM) carbine stock" the MOE SL-S (Storage) Stock is a direct replacement buttstock for AR15/M4 carbines. The sleek profile" dual-side release latches" and waterproof battery tubes make it the slimmest storage tube stock available. The SL-S provides an enhanced cheek weld and true" O-ring sealed" 10m waterproof storage area desired by many" but fits it into the narrowest package possible to allow a more upright head position and minimize bulk. A rolled toe and angled rubber butt-pad are optimized for use with body armor" and an ambidextrous QD sling swivel socket is included. A unique leaf-spring tension system provides a solid fit on mil-spec receiver extensions" with slightly less friction than the original SL. The MOE SL-S is the most intuitive" comfortable" and efficient storage stock available. Made in U.S.A.
Features:
Two water-resistant battery storage tubes
Sloping cheek weld combines a slim profile with user comfort
Internal anti-rattle leaf spring