Good question, High chance that It may need cored. Even with another self centering insert being in a shaft, such as a 5/16-18 or 5/16-14, the barrels tend to run a slightly larger diameter, and with the Uniloc setup It is so tight and precise that even a small amount of run out will transfer into the shaft quite a bit, and I would rather start out with a fresh canvas, so that I can properly control the bore to fit the insert, and not have to try to salvage a old bore and make It work.