According to police, the guns were found during a raid of the famous outlaws' hideout in 1933.
The Missouri family that owns the guns say a police officer gave the weapons to their great grandfather as a gift.
"It's hard to put a value on something like this," said auctioneer Robert Mayor. "At the end of the day, we like to say it's worth what someone is willing to pay for it."
Both weapons were sold to an online bidder.
Before the auction, the guns had been kept at a police museum in Springfield, Mo.