can a ruger #1 in .243 be rebarreled to a magnum caliber such as the 300 RUM?

Yes all you need is a barrel and different extractor all #1 actions are the same.Ben Forkin in White Sulphur Springs is a knowledgable Ruger #1 gunsmith.w/regards

JD (SSK Industries) did a great job on my #1 (rechambered and trigger job). I know he rebarrels too. Top drawer work. Good luck.

Gary

FWIW, A couple of years ago I inquired of SSK about rebarreling a #1 in .243 to a larger caliber. They told me that, while the breeching is the same for all, the location of the fore-end hanger is different on the various models and is not easy to adjust. Therefore, they recommended a caliber that would fit the contour of the original barrel. You may not have any problems, but...