I recently got a Oneway coring jig, and watching the video that came with it noted recommendations for a tailstock extension while coring. I thought that prudent seeing how a lot of damage can happen if a blank gets loose while coring. I didnt have a mt extension per se but found an 18mm deep socket fit over the threaded end of my Oneway live center and had a very long drive extension in the toolbox. It took some minor adjusting to center the end in the cored blank and it worked quite well.