Realism. (not briefly) (S.T.A.L.K.E.R.: Shadow of Chernobyl)

Decided to make a realistic knockdown in Stalker PM. According to some reports - to kill a man need energy 10 j (joules) per 1 kg of live weight (found out on the forum). In the game Stalker weighs 90 kg. to kill him you need 900 j (suspended). Bullet energy 300 j PM. - 900 : 300 = 3 shots to kill a Stalker. But it is too short - 3 shots so I multiplied the goldmedalist Stalker 2, i.e., 1800 j and 6 shots. That would kill with one shot need the value of outstanding 1, on this basis: 1 : 6 = 0.17 is the value of knockdown for PM. Tell me, is it relatively realistic? Of course you can take into consideration the length of the barrel that affects the energy of the bullet.