"Spring-loaded rifle stock; adjustable tension springs absorb a significant portion of a weapon kick, resulting in more controllable recoil."
RE93 Absorbing Stock description (from Aliens: Colonial Marines - Arsenal Upgrades - NSG 23 Assault Rifle - W-Y RE93 Absorbing Stock)
The W-Y RE93 Absorbing Stock is a spring loaded, shock-absorbing rifle stock that manufactured by Armat Battlefield Systems for the NSG 23 Assault Rifle.