For an AR-10 chambered in .308/7.62 with a collapsible stock, if it has an AR-15 carbine buffer tube (which is 7” long on the inside) then it needs a 2.5” buffer and we recommend the KynSHOT AR10 2.5” carbine hydraulic buffer “Shorty” (Part# RB5004) and an AR-10 carbine buffer spring, either the JP 308 carbine buffer spring (part# JPS-OSC-308) or the SPRINCO AR-10 carbine buffer spring (color code ORANGE - Part# SPRINCO-25762). If your rifle came with a 2.5" buffer and you have not changed your buffer tube, then this is what you need.
https://www.blitzkriegcomponents.com/hydraulic-kynshot-recoil-buffer-308-carbine-25.html