He was represented in court by Peter Glenser who is one of the country’s leading barristers for firearms law and a member of BASC’s council.
BASC’s director of firearms, Bill Harriman, was called as a defence expert.
Mr Thomas, who plays for Chester Rugby Club and Northern England, had argued that he was covered by his father’s certificate.
The court heard that Mr Thomas had taken his father’s gun to an upstairs window with his father’s consent to shoot a rabbit he saw in his parents’ garden, where his father had a vegetable plot.
His father, Professor Andrew Thomas, was downstairs at Higher Berse Hall, Southsea, Wrexham.
Professor Thomas said he considered that he was present and would have been able to shout up to his son as he shot the rabbit if, for example, he saw someone approaching the property.
Mr Thomas shot the rabbit twice but said the shot was very safe because of the back-stop, with the bullets going straight into the ground.
Armed police arrived and arrested Mr Thomas after members of the public nearby complained.
Peter Glenser said in court the trial was a “gross overreaction” to what had happened.
Bill Harriman said: “BASC’s expert departments are here and can offer advice to members. We’ve got a long track record of doing this.”