![1girl antenna_hair battle_rifle bayonet breasts brown_eyes brown_hair commentary_request fingerless_gloves gloves gun highschool_of_the_dead holding holding_gun holding_weapon large_breasts long_hair looking_at_viewer m-21 m14 miyamoto_rei plaid plaid_skirt prime revision rifle school_uniform scope shirt skirt sniper_rifle solo taut_clothes taut_shirt weapon rating:s score:9 post #2675906](/cdn_image/preview/42/60/4260b806c2365130d6cd3f785ff34b08.jpg)
The M-21 Sniper Weapon System is a semi-automatic sniper rifle used by the U.S. military. It is based on the M-14 and fires 7.62x51mm NATO ammunition from a 20-round box magazine. It's basically a match-grade M-14 with a scope.
This tag implicates sniper_rifle (learn more).