For an AR-10 chambered in .308/7.62 with a fixed stock and full length/fixed stock buffer tube, we recommend the KynSHOT AR-10 Rifle Buffer (Part# RB5006) and the JP 308 Rifle Buffer Spring (JPS-OSR-308). This set up will work well for any caliber in this configuration such as 6.5 Creedmoor, etc.
https://www.blitzkriegcomponents.com/hydraulic-kynshot-recoil-buffer-308-fixed-stock.html