Although the .50 BMG round was based on a light anti-armour round, modern MBT's are pretty much impervious to everything but other MBT's or LARGE shaped charge warheads. To engage a tank from a distance with a Barrett, SOP is to shoot for the vulnerable spots; radio whip aerials, Thermal Imaging sights, IR searchlights, vision blocks if you're desperate, but the best target of all it the tank's brain which sticks up through the open cupola and is unaware of the SF AMR team lurking in the bushes 800 yards away, picking off track commanders and whip antennas starting with the rear AFV and working their way forward up the column til someone notices that Joe-Bob ain't responding on the net...
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"..but never ever Fear. Fear is for the enemy. Fear and Bullets."
10mm: It's not the size of the Dawg in the fight, it's the size of the fight in the dog!