Not an unexploded bomb
During WWII Ashley Walk was used as a testing and practice rang for live and inert air dropped ordnance. After the war the site was cleared by the MOD before being opened up and returned to its original use. Over the years however, some (possibly live) ordnance has been found by the public and these finds are dealt with by the police and the MOD Bomb Squad.
In 2016 this large metal item (48cm diameter) was reported by a member of the public as a possible unexploded bomb on the range and this has now been investigated. Thankfully it is thought that this is not an unexploded bomb.
The Forestry Commission have been in touch with the police who have verified that it is not ordnance (to their knowledge), they thought it was a water bore hole outlet of some kind. Another possibility suggested by FC is that it could have been a marker beacon of some kind for ranging.
Further Reading
The Ashley Range Overview page contains a series of links to pages about the other targets on the range.