I purchased a 6mm 30-30 AI barrel for my TC from VVCG about a month ago and have just now really started working with it. Far and away the most accurate gun I have ever shot and I haven't had many opportunities to work with it. Kind of a PITA to make up cases for the first time around but once that part is complete is works well.
No real difference between
6mm 30-30 Imp.
6mm 30-30
6mm Classic
6mm Bullberry
6mm Bullberry Imp.
etc.
Improved versions are said to have a better case life and reduced backthrust on the frame. But performance wise there is no difference.
Makes a great carbine for a TC contender with a 22" full bull barrel.