Nope not an M-21 or DMR
i'm betting not even of military origin (for the pic that is)
the gun IS a Garand with a side mount scope. it may or may not be a legit C model (D's have a distictive flash suppressor, gun in pic is without ANY flash hider, thus not an M-14/21 variant either) . so many fake "Sniper" garands were garage gunsmithed up using a standard unaccurized M-1s and surplus scopes and mount kits, that it's become hard to tell genuine from "franken-sniper".