The belt has nothing whatsoever to do with whether or not the cartridge is reloadable. The belt really serves no purpose other than being decorative. Granted, case life, as is the case with most ultra-high pressure cartridges, is not always very long (3-5 loadings with near max loads), but it's no different than the belted Weatherby. If your friend is a handloader, and his cases are hard to extract, then he needs to back the charge down a grain or two. If it's with factory ammo, then he probably has a tighter than normal chamber. The RUM's are hot cartridges, and brass isn't going to last very long with the pressures that they run. Cost of high performance.
Mike