They redid the test in a later episode, using a PU scope. Bullet went through, somewhat.
Biggest error, though, is they did not duplicate the terminal velocity of the 173gr bullet at roughly 800yds. (They were using a 150gr M2 at about 50-100yds). Perversely enough, as velocity gets lower, often penetration goes up! They proved that on the show several times, but ignored it in this test...
FWIW according to the book SGT Hathcock was only about 200yards from the enemy sniper when he made the shot.