If you are tired of not having fast weapon switch for most HL1 mods then please use this bind, simply open Steam console whilst in HL1 game by using the ~ key and type this up - one in each line:
Code:bind "MWHEELDOWN" "invnext; +attack; wait; wait; -attack"
bind "MWHEELUP" "invprev; +attack; wait; wait; -attack"