morddwyd is right - there can be no doubt about the fact that the original conviction was sound. This man was in possession of an illegal firearm and a large quantity of ammunition, and he pleaded guilty.
The fact that he may have been wrongly advised about his plea is a separate matter entirely, and the original trial judge can't be blamed for it.
The sentence has been reduced on appeal, and that's an illustration of the justice system working properly. What happens now is up to the justice system again - an appeal against conviction seems to me to be a rather misguided policy, in that there is no doubt about the fact that the man possessed a firearm and ammunition illegally. He may be of exemplary character, but a criminal offence is a criminal offence, and good character usually mitigates with regard to the sentence, not the conviction.