The Australian Border Force seized the black market guns, as well as 43 firearm silencers and 37 kilograms of gunpowder, after raiding more than a dozen properties.

A Border Force spokeswoman said certain types of bullets and parts to make silencers were also found.

However, she said it was unclear where the illegal goods were heading.

"The investigation is still ongoing," she said.

"We will have further information, but we are unsure what they were to be used for."

After receiving information from US authorities, Border Force investigators identified a large number of Australian customers buying "solvent trap" cleaning kits from a US-based website.

Items in the cleaning kits can be easily converted in sound suppressors, or silencers.

Assistant Commissioner Wayne Buchhorn said Border Force had a range of tools to track illegal guns, and locate those behind them.

"Between local and international intelligence sharing, our world class firearms detector dogs and cutting edge X-ray scanning technology, we are well placed to pick up these items at the border, no matter how they arrive," Mr Buchhorn said.

He said the community, including legitimate gun owners, were encouraged to help combat illicit firearms.

"We don't want to be penalising recreational shooters, so it's important firearm owners who buy parts and accessories online are aware of Australia's strict firearms regulations, and that if they attempt to import prohibited goods they face losing those goods and will face possible criminal prosecution," Mr Buchhorn said.