[Muhlex]

Im pretty sure Valve implemented this with a "viewmodel" particle effect, which you could send to the Client yourself via Temp Entities or an info_particle_system. You might need to check CS:GOs .pcf files to see if it's in there though and won't be able to customize that without a custom pcf file, probably (except for the off-chance that the particle effect supports an input by the particle system, which determines the duration of the effect).