.50 Cal
From ARRSEpedia
An absolute beast of a round. Used mainly in the M2 HMG and purpose built sniper rifles such as the M82 Barrett. Civvies believe the .50cal bullet has so much power, it'll travel miles and miles, punch its way through several stonemason's yards, through the odd T-72 tank before blowing someone's head off. Not too far from the truth really...
