It's inherently impossible for a real weapon to be unrealistic, but a weapon as powerful as a semiautomatic .50BMG rifle is extremely difficult to implement because it's very difficult to accurately capture the Barrett's disadvantages (extremely bulky and heavy) along with its advantages (long range, devastatingly powerful round and relatively high rate of fire).
Most games would solve this by taking away some of the real advantages or adding made-up disadvantages; an ultra-realistic game like Infiltration can't do that, so it simply doesn't put the weapon in until such time as the technology of the day can simulate the disadvantages properly.
Most games would solve this by taking away some of the real advantages or adding made-up disadvantages; an ultra-realistic game like Infiltration can't do that, so it simply doesn't put the weapon in until such time as the technology of the day can simulate the disadvantages properly.