The incident forced South Street, Abbey Road, Eastgate and Spalding Road to be closed while the scene was made safe.
The incident was concluded around 5:15pm after Lincolnshire Police’s Explosive Ordnance Disposal found and removed a spent shell.
A statement from Lincolnshire Police said: “The incident reported a few hours ago in Bourne Road, Bourne is now concluded.
“EOD confirmed it was a spent shell and have taken it away.
“All roads are now reopen.
“We’d like to thank the public for their patience.”