***Then, assuming we’re seeing actual pics of the counter sniper, he was shooting something bigger than .223, which would be smart since they would want to be able to outgun the random dumbass.
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IIRC, the Secret Service Sniper/Counter-Sniper Teams use .300 Winchester Magnum or .338 Lapua.
To be blunt, at that range not much should be left of the target’s noggin...
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Yup: I was looking at the stick mag in the available pic and , from here , it looks like an AR-10 frame which would be .308. Lots of that around. But as you note, at Quantico, they train with not just 308 but 300 WM as well as 338 Lapua. The dummy’s head would not constitute enough of a mass to expand a soft point but any convenient ball round would be spectacularly fatal.