One of the most popular outlets for selling many of the parts to build an AR-style rifles says it has rules banning the listing of so-called “assault rifle” components, adding its regulations are in line with laws in its home state of California.

But a news investigation into the sales of AR parts on the world’s most popular auction site eBay shows many sellers either don’t know the rules or tweak their listings to circumvent algorithms alerting the company of the banned items. And despite officials at the company learning of the parts sales, the items remain on the site for weeks despite the rules.

“This violates eBay’s policy banning the sale of ‘parts or accessories for assault weapons,” the Center for Investigative News’ Reveal wrote. “The policy is closely tailored to match California law, which is among the nation’s strictest. But the company’s automated filters and user-flagging system fail to stop it.”

According to Reveal, AR parts sellers who know about the ban rewrite their listings, calling items “rifle barrels” or “rifle parts” rather than “AR-15” parts.

“The buyer has to know what he’s looking for, and the seller has to be careful to not advertise that it fits an assault weapon,” one seller told Reveal. “If you have a part that’s compatible with a number of weapons platforms and you don’t mention that one of them is an assault weapon, my understanding is that you are good to go.”

But a search of eBay by Shooting Sports Retailer shows listings such as “AR rifle barrel carbine 16 inch” and “5.56 10.5’ AR pistol barrel.” The site does not sell AR-style rifle lower receivers, which are the “serialized” part of the rifle and must be transferred through a licensed dealer.

“Getting around eBay’s automated filters can be as easy as inserting a space in an advertisement,” Reveal says. “Changing the brand name Magpul, a company that makes AR-15 parts, to ‘Mag pul,’ for example, can be the difference between an item being removed and it selling.”

“A technique gun parts sellers say they often employ is to not mention an item’s compatibility with assault weapons, even if it is designed explicitly for that purpose,” the story adds.

Many firearms retailers use eBay as part of their virtual sales portfolios, with some seeing as much as 20 percent of their bottom line coming from listings on the site. And eBay has become a boon for AR builders who use the site to shop for hard-to-find parts at competitive prices.

An eBay spokesperson declined to comment on the Reveal story but said the company “took appropriate action against the sellers” of some AR parts.