 Complete the following phrase:  The side, rear and top armor protect the BMP-1 from 7.62 mm small arms fire from most distances as well as smaller artillery shell fragments, but do not protect the vehicle against 12.7 mm heavy machine gun fire from close distances or larger artillery shell fragments. Nevertheless, ground tests demonstrated that rear doors with their fuel tanks filled with sand withstood hits from standard 12.7 mm rounds. In Afghanistan and Chechnya, armor-piercing 7.62 mm rounds fired from general-purpose machine guns at ranges of around 30  50 m sometimes penetrated the rear doors and hatches. During the 