Aha, you had it shortened. That's not too surprising then. Bores are often not quite straight, it may be centered at both ends but if you cut it you may find the bore wanders off center in the middle. That is not desirable but does not mean it won't shoot OK, it should shoot at least as well as before it was cut, though likely not to the same point of impact. I would say that 16" seems awfully short for a .243, you'll probable loose 300 fps and if accuracy is not as good as before I'd blame the shortening rather than the off-center bore, after all, it was always off center, you just didn't know it before.