Hi,
I don't have any further information on James Hammet, except that he is buried in the churchyard at Tolpuddle which I assume you know. However Edward John Eyre to whom he was assigned became famous as an explorer in Australia and Lake Eyre and the Eyre Peninsula in South Australia are named after him. His property, a sheep station outside Canberra, was in a very remote area for those times. Do you have any details of James Hammett's pardon (I understand it was a Royal Pardon) or when he returned to England.
Also the lottery system for assigning convicts was instituted by the Government as the demand for labour to establish properties was so competitive and not enough workers to go around. When the convict ships arrived the names of all people wanting convict labour were put into a barrell and drawn out, hence the "convict lottery".
If your James Hammet did anything to earn himself a colonial sentence the information would be in the Colonial Secretary's Correspondence which, after 1825, has been indexed by Joan Reece on fiche. It is not online. I don't have access to this index but someone else may be able to look it up for you.
Andcarred