Motorists faced lane closures on the A43 yesterday, Monday, December 17, as police officers searched for missing bullets.
During the early hours of the morning firearms officers answered an emergency call at the roundaout on the A43 south of M1 junction.
During the incident a box containing bullets which had been left on the roof of a police car fell into the road.
The box was recovered by five bullets remain missing.
Lanes were closed throughout the day in order to protect officers and police dogs carrying out the search.
In a statement a spokesman for Northants police said the search was now complete but added: “It is possible that the remaining few bullets could have been carried a distance in the tyres of large vehicles.
“Our priority is the safety of members of the public.
If anyone finds or sees anything they suspect to be a bullet they should not touch the item and should immediately call 101.
“Northamptonshire Police takes the security surrounding armed police and their equipment extremely seriously and this incident will be thoroughly investigated.
“The incident has been voluntarily referred to the IPCC.”