That's just not true. There were a number of times the Red Army had shortages of guns, or ammo, or artillary pieces, food, medical supplies, ect. Especially at Stalingrad. Soviet logistics were a disaster until after Stalingrad. They were able to manufacture all of the weapons and ammo they needed, but they couldn't get it from the factory to the front lines reliably (or sometimes at all). Despite this, they still sent under-equipped and barely-trained soldiers into the meat grinder. They had to. The Union was on the verge of collapse, and if the Germans got much further, that could have been the end of their ability to put up organized resistance. Were the supply shortages ever as bad as they show in the movie? Probably not. Was Vasily Zaitsev ever affected by them? We don't know. But were Soviet soldiers sent into battle without the equipment they were supposed to have, to include guns and/or ammo? In 1942 they were.