You can weigh them on a scale that measures troy ounces. There was a 'tube of some guy who showed real and fake 1oz rounds. The fake ones registered .7 troy ounces or so.
I didnt even need those tests. You can tell the fake one by the crooked stamp! Engelhard (or any reputable silver miner/minter) would not allow a crooked printed bar like that to go out the doors, particularly for a 100oz.
It's not just the fake looking ones that are the problem. People take real bars and hollow them out and fill them with lead. The ultrasound test would be useful for such cases.
