Minecraft code sends velocity packets from server to client to notify them of entities' velocity. This however have limitations, since velocity is clamped between -3.9 to 3.9 (presumably blocks per second) and is transferred using short. Said limitations would cause clientside fast projectiles to be rendered terrible innacurrately even though it lands perfectly on server side. This mod coremods vanilla velocity packet system, so it does not clamp the value and send the values using integer instead of short.
