Depending on angle and range .50s will have a hard time penetrating side armour of the turret . If you shoot vertically into turret you will wreak havoc though. Also even if some bullets penetrate and kill some of the crew members . if just 1 of the crew are alive wirbies can still shoot and reload the gun, with some longer time in between. The One guy that is hard to hit is the driver that crawl up to turret and continue to fire.