danb
dont be a dumbass
It has the HB profile. I have both HB's and A1 profile uppers and you can tell visually. If need be, the manufacturer can state "Heavy Barrel" on the receipt.
Website says that 16-inch barrel weighs 1.9lbs, which I would say is a "heavy barrel". Considering their M16A2 20" barrel comes in at 2.05 pounds.
Visually is not good enough. Does not matter if its 400lbs and 15 inches in diameter.
It has to be MARKED or MARKETED (advertised) as heavy barrel. If they give you a receipt that's ok, most don't give a rats ass about Maryland though (buy it, or don't). But it should be in writing.