original_query: What were the changes made to the gas block during the production stages? What is the most relevant chunk to answer the query?
query: What were the changes made to the SKS rifle's gas block during its production stages?
answer: The SKS gas block underwent three changes: the first (1949-early 1950) was squared-off at a 90-degree angle; the second (late 1950-1951) was cut at a 45-degree angle; and the third and final stage (1952-1956) was curved inward slightly toward the action.