Fired at the muzzle, a representative 6.5 Creedmoor load (9.1 g, BTHP, 800 m/s) reaches roughly 36 mm (1.4 inches) into aluminum 6061. That is enough to defeat a typical barrier of this material — treat anything behind it as exposed.
About Aluminum 6061
Aluminum plate (~6 mm), as found in light vehicle and aircraft skins.