Blueprint above contains line trace with start point from weapon socket to scaled forward vector from it. That forward vector will not match crosshair projection because it is not depended on it. The end of trace from weapon must be determined by another trace from center of the screen. Additionally your setup depends on how you manage fact that camera can observe something that trace from weapon cant hit properly. For example when character is taking cover behind wall. That remind me an article from Gamasutra about TPS aiming
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