He was found guilty in May 2011 of causing criminal damage to the vehicle, and given an 18-month conditional discharge and ordered to pay £1,800 in compensation.
He has now successfully appealed against the verdict at Bristol Crown Court.
Mr Gentry-Long said: ?No motive was ever established for a responsible pensioner with more than 50 years of safe firearms handling suddenly to take random potshots at a friendly neighbour?s property.?
?This was an appalling miscarriage of justice, and the past 18 months of my life have been a living nightmare. I am utterly ecstatic at this outcome of the appeal.?
Mr Gentry-Long was locked in a cell for seven hours before the charges were made, and later had his air rifle, other guns and ammunition seized by police, who revoked his firearms certificate.
However, during his appeal, a firearms expert said he believed the damage to the caravan could not have been caused by shots from Mr Gentry-Long?s air rifle.
Mr Gentry-Long said: “I felt deeply aggrieved at being accused of an offence I had nothing to do with, and of being convicted despite evidence to the contrary.”
“The police?s handling and presentation of evidence can be most kindly described as deeply disingenuous.”
His solicitor Matthew Graham, from Mowbray City Advocates, described the case against Mr Gentry-Long as ?hopeless?.
He said: ?Mr Gentry-Long always maintained his innocence and has finally been rightly vindicated. A circumstantial prosecution case collapsed in the face of forensic examination of the evidence.?
?Any investigation should follow all lines of enquiry. This one didn?t and wasted time and heartache has followed.?
Inspector Steve Mildren, of Avon and Somerset Police, said: ?We received a report of criminal damage and carried out a thorough and professional investigation. On the basis of that, the Crown Prosecution Service decided that a charge should be brought. We respect the decision of the court.?