I can be safe to say, nobody here has fired or disassembled, let alone carry a Barrett M107 or equivalent. Heavy as sin, and not the most accurate of rifles to a point. Unless you're a serious shooter, leave the .50 BMG alone. Buy a Remington 700, throw a Harris bi-pod on it, and a nice 3X9 scope. You'll be tickled pink with a .308 or 300WSM, hell a .270 aint bad for what it is either.
Basic good shooting rifle
http://www.snipercountry.com/photogallery/Rem700PSS_SightronSII4_16x42MilDot.jpg