For reasons elaborated in The Final Truth: Solving the Mystery of the JFK Assassination, the answer is... during the second shipment from the Dallas Police to the FBI five days after. To assume it was damaged when Oswald first received it is to underestimate his acumen as a USMC-trained marksman. Why would he keep a damaged, defective and “misaligned” scope on the rifle during eight months of use? In truth, he knew it was working perfectly on 11/22 and he used it for all three shots, including the first zeroing shot.
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