I think whether this is possible or not entirely depends upon the thickness of the AR500 plate being struck, the distance and the type of round and it's speed. Most AR500 plates sold in retail stores at least around me are not thicker than .375 inches. This can not stop a typical 50 cal round from 200 yards or less, at 700 yards these bullets slow down a good bit so it's possible, hard to say.
But it's useless debating these things unless you know the thickness of the plate, the distance and the speed. Some people are posting videos of inch thick AR500 plates, I have no idea where they are getting them, but apparently someone out there makes it, and yea, that'd probably stop a 50 cal at much closer range, but it does no one any favors to say this steel or that steel, or this piece of titanium or that piece of titanium can stop a 50 cal unless you know the thickness and the distance.
There's also bullets that go much faster than 50 cals, for instance the rifle used for testing in this thread fires rounds that go between 3150 to 3200 fps and keep a higher percentage of that velocity at longer distances because of the shape of the bullet.
