crash is 100% right, my gunsmith, Wayne York, has rebored/rechambered many, many rifles to .338-06, it's one of his all time favorites, but when he did mine, he couldn't chamber the A-square rounds, he had to lengthen the chamber neck to allow them to work, he had to open it up a tad too cuz the brass is thicker. Necked up dummy rounds of .30-06 and .270 brass chambered fine before he made the changes.
Tim