Also ask him why service rifle shooters use pretty much the same 'come ups' (elevation adjustments) out to 600 yards whether they are shooting the US .30, the 7.62x51 or 5.56x45. Yes, the 5.56 starts out a little faster, but the .30 bullets are a bit slipperier which evens things out downrange. If the 5.56 bullets were fired at nearly 3x the velocity of the .30s as your instructor said, this wouldn't be true.