It has been authenticated by its London-born designer Roger Christian who won an Academy Award for his production work on the blockbuster.
He based the blaster on an antique German pistol, a 9mm Mauser C96.
Roger, 81, commented: "I have seen several purported Han Solo blasters over the years which I could not authenticate.
"This is the first blaster I have seen that is consistent with the features of my original and with documentation to back it up which bears the serial number on this Mauser."
Top film historian Marc Wanamaker, a consultant to 20th Century Studios and the Academy, said: "This is one of the most iconic props to come to auction in the last 10 years and should fetch at least $2.5million at auction."
It comes up for sale on ...