Parts of an AR-15 semi-automatic rifle were concealed in a Bluetooth speaker and sent from the United States to Sydney, federal police say.
The discovery of the illicit package in February sparked a counter-terror investigation and led to the arrest on Wednesday of a 48-year-old man at his Merrylands home.
"An AR-15 is a semi-automatic rifle that can enable someone to fire off dozens of rounds quickly, and is an item that has no relevance or use for someone living in a city," Australian Federal Police assistant commissioner Scott Lee said in a statement.
"Keeping illicit guns from the streets is a priority for police because of the dangers they pose in the hands of criminals."
Mr Lee said NSW's counter-terror team began investigating the import "out of an abundance of caution" but no links to terrorism have been found.
The rifle parts importation was later linked to an air compressor, which had about half a kilogram of methamphetamine concealed inside.
Merrylands man Joseph Moujalli faced Fairfield Local Court on Thursday charged with importing prohibited parts and importing a marketable quantity of border controlled drugs.
He was granted bail ahead of a court appearance in December 11, on conditions including daily reporting to police, a nightly curfew and use of only one mobile phone.
His mother also deposited a sum of $2500 and Moujalli agreed to forfeit $5000 if he breaches his bail conditions, court records show.
A Georges Hall man, 33, arrested in April over the methamphetamine seizure is also before the courts.
Investigations continue into the origin of two pistols seized on Wednesday from places associated with the AR-15 importation.
Approximately $27,000 in cash and a number of high-value watches were also seized, which police allege are the proceeds of crime.