Qantas will very strictly enforce the carry-on limits (size) on domestic flights. They are a little more relaxed with premium cabin international services. The limted are published here on the QF web site.

QF are renowned for being oneof the strictest airlines when it comes to carry-on limit enforcement. Their checked baggage service is generally pretty good as far as airlines go - but they do have problems with lost, misdirected or damaged luggage from time to time, so make sure you have appropriate travel insurance and pack according to the items you are taking.

As has been noted, Australian gun laws are also strict and will be enforced on entry to the country, so check it out first and make sure you have all the correct paperwork needed.