Vltor Carbine Modstock Combo Kit - This modstock was developed from ideas and input from both firearms designers and end users to help the operator better prepare for any mission. A pioneer design, the Modular Firearm Buttstock (Modstock) aids the operator and succeeds where other stocks have failed. The Modstock does not stop with the mounting of accessories; it is truly a system of solutions. The kit includes a 5-position, mil-spec receiver extension, buffer, spring, receiver extension lock plate and lock plate castle nut.