FN M240 Collapsible Buttstock and Buffer Assembly. This adjustable steel and polymer butt stock contains the hydraulic buffer. This assembly can be used on the 7.62x51mm M240 family of machine guns. This includes the M240B, M240L, FN MAG, and FN MAG 58 manufactured by FNH, FN Herstal, FNH USA, or FN America. This is a factory original FN part made to the same high standards as the parts already in your FN firearm. FN America factory parts and accessories are made with the same quality in materials and workmanship that you have come to expect and trust from FN America.