You mentioned calibre only but Bob the sheister gets my vote for a semi auto platform, especially if you will be taking shots seated... no need to work that bolt, and fast follow up.
One thing a right handed American and a left handed Australian/South African has in common is the driver side shot favours both. On the carrot farm behind my place, this has become a popular option .. but I still need to work a bolt due to politics ... miss those days in South Africa when I had a Colt 223..
