Half-Life 2's gun viewmodels aren't modeled on the other side because you're never going to see them during normal gameplay, but in VR you can freely move your hands around and that's why you can see the missing parts.

引用自 max：

Half-Life 2's gun viewmodels aren't modeled on the other side because you're never going to see them during normal gameplay, but in VR you can freely move your hands around and that's why you can see the missing parts.

^ this and also, to have the gun fully modeled albeit lower res, enable world models for weapons or something along the lines of that.

If you dont like it being low res but want to see both sides, use a addon that has the guns, best ones i recomend are probably catse's ones. and for the rest just use half life 2 vr weapons remasterd, very cool