I'd seen that some time ago, but forgotten about it. Thanks for posting.
In his book "The Ultimate Sniper" Plaster gives a chart detailing some the penetration capabilities of different rounds. The 50 BMG can do some pretty interesting things. On our informal home tests, we found that partially decomposed granite (which is common here in the Northwest) stops .50 BMG AP pretty well, compared to other things you might pick up at, say, a machinsts auction. We were picking the steel cores out of the large rocks with our hands, or prying them out with small knives. But that was using a .50 BMG "Carbine". The M2 will give better velocity.
That reminds me of my son, when he was about 6, busting up basketball sized chunks of basalt with a carbine-length .30-30 Winchester model of 1894. Ah, freedom!