If you have a domestic QF flight in J your allowance will be 3 bags (including the OWE benefit). Your ticket should indicate the correct allowance for all flights. And, if your ticket was issued after 26.02.13 QF moved to weight concept on some international flights (40kg + 20kg as OWE). If QF is the MSC in your itinerary its allowance may apply to the entire journey. Your ticket will state the correct allowance.

In my experience when BA issues the ticket and if BA is the first carrier they indicate their allowance for the entire journey for all carriers on the ticket.