The bat Babe Ruth used to swat his 500th home run could set a new auction record.

Bidding on the Louisville Slugger opened Wednesday at SCP Auctions and already reached $517,846 with 16 days remaining.

Ruth hit his 500th career homer at Cleveland's League Park on Aug. 11, 1929, becoming the first player to achieve the feat. He later gifted it to his friend, Jim Rice, the former mayor of Suffern, New York.

SCP Auctions believes the item could break the record for the most expensive bat sold at auction. The record currently belongs to the bat Ruth used to hit the first home run at Yankee Stadium in 1923, which sold for $1.26 million in 2004.

"We're estimating this at ($1 million) and up just to be conservative," SCP Auctions president David Kohler told Steve Keating of Reuters. "We think it will surpass the other bat. This 500 bat is kind of the brother to it."

He added: "Even though he has been gone since 1948 he remains the king."