The sculpture is titled "Yininmadyemi", the indigenous word, meaning 'Thou didst let fall'. As the two interpretative 'signs' near it state, it relates to the indigenous Australians who went to war for Australia in the 20th century, many not getting the recognition of other veterans. While there is a very true figurative explanation, as from the nearby signs, the following technical drawing shows just how close the artist got the ginormous representations.
Technical Drawing of .303 cartridge [ex-Wikipedia, British .303]
As mentioned, nearby are two plaques that explain the figurative nature of this sculpture. A large one is engraved into the base of a 'discarded' cartridge, as follows:
YININMADYEMI
Thou didst let fall
"Aboriginal and Torres Strait Islander people have always
defended their country. Indigenous Australians are known
to have served in the state colonial forces before Federation
and have proudly carried on this tradition of service.
"Aboriginal and Torres Strait Islander diggers experienced
the horror of war on the battlefield and many made the ultimate
sacrifice. The sad reality for these veterans was that equality
in the country they fought to defend remained a distant dream.
"This memorial on the land of the Gadigal clan pays tribute
to all Aboriginal and Torres Strait Islander people
who have defended our country - the unsung heroes,
our brothers and sisters, our mates.
We remember those fallen
We honour those standing
Nearby (to the north) is a round cast bronze plaque placed by the 'City of Sydney' with the cast text milled, so that the black textured background makes text readable. The inscription is:
YININMADYEMI Thou didst let fall
Tony Albert
"YINIMADYEMI Thou didst let fall is located near the historic site of a ritual contest ground on Gadigal land. The artwork honours the bravery and sacrifice of Aboriginal and Torres Strait Islander men and women who have served their country.
"Inspired by the story of the artist's grandfather, Eddie Albert, YININMADYEMI Thou didst let fall comprises four standing bullets to represent those who survived and three fallen shells to remember those who made the ultimate sacrifice.
"Unveiled by Lord Mayor Clover Moore 31 March 2015"
By the way, a quite similar presentation of .303 selected cartridges is shown on the Wikipedia page for the ammunition, as follows:
Various forms of British .303 Wiki
Location: Hyde Park (near Elizabeth Street and Bathurst Street), Sydney, NSW - available 24/7
Visited: 1119, Sunday, 19 January, 2020