Question: If Jude Law as Vasily Zaytsev is the protagonist, then why is Joseph Fiennes the first-billed actor of the movie?
Answer: For the same reason Marlon Brando and Gene Hackman were top billed in Superman. He was a bigger name and his agent was able to negotiate a better deal.
Answer: They almost share the same amount of screen time, but Jude Law is a tad younger and Joseph was coming off a very successful 'Shakespeare in Love' as well as 'Elizabeth'. He was a more marketable actor at the time.
Chosen answer: Vasily Zaitsev (Jude Law) uses a 7.62 x 54mm Mosin-Nagant M91/30 rifle with a PU scope. Major König (Ed Harris) used a 7.92 x57mm Mauser Karabiner 98 K with scope. Law's scope was wrong as the model used in the film wasn't available until after the Battle of Stalingrad.
Grumpy Scot