If you mean the animation on what you see on a player, what you use is to animate the view model ( v_ ) of the weapon, nothing to do with p_ model which is handled by the player's model. Since it's a custom weapon, you have to force to play an animation on the player. ( animation which is near on what you need ). Basically hooking CBasePlayer::SetAnimation() in post, then playing with pev_sequence, pev_frame and ResetSequenceInfo(). There is a plugin I've posted in the resquest section ( Prone Position ) which use such forward.