It seems it's only for player/monster. When you look at the HLSDK ( single player ) it uses mainly for monster.
By the way, what do you want to do exactly ? If you want to to trace a line from the weapon attachment, you have to use for example, if attachment is 1 : id | 0x1000
EDIT : Example, I remember creating the Shock Rifle weapon ( like in OP4 ) and to show lightning between each part to the center ( see the model below ), I'm using ( it uses TE_BEAMENTS ):
Code:
FX_BeamEnt( id | 0x2000, id | 0x1000, gBeam, 1, 8, 50, 200, 6, 0, 10, { 200, 200, 255 } );
FX_BeamEnt( id | 0x3000, id | 0x1000, gBeam, 1, 8, 50, 200, 6, 0, 10, { 200, 200, 255 } );
FX_BeamEnt( id | 0x4000, id | 0x1000, gBeam, 1, 8, 50, 200, 6, 0, 10, { 200, 200, 255 } );