It's common for rimmed and belted bottleneck cartridges to stretch a lot during firing. This is because, in order to control headspace with the rim, it is necessary to prevent any chance of the shoulder making chamber contact before the rim does. For this to be guaranteed, the shoulder tolerance has to allow for the combined headspace and rim thickness tolerance as well as its own. Thus, to allow for the worst-case chamber, the sizing dies for these cartridges tend to set the case shoulder back more than is strictly necessary for the average chamber. That, in turn, results in extra case stretching.
The solution for most belted and rimmed cases is to size them so they headspace on their shoulders instead of on their rim or belt. But I don't know how well that would work with the Hornet's gradual shoulder taper.
