It looked like a 0.50 cal (M2?) with a telescopic sight. I don’t think the sniper had any better target than his mouth. The witness interviewed by the BBC, the witness who tried to notify police and the Secret Service, said that the Secret Service “blew his brains out”. An assertion that assumes a fact not in evidence.
I have heard reports that the Secret Service sniper requested permission to “engage” 42 second prior to Crooks’s first shot but was denied. Once Crooks fired, apparently different ROE came into play.
Not 50— 50 would have left no face to see at that range.
More like 308 fmj non exploding.