The 6.5mmx52R (6.5x52R) is a rimmed cartridge, still loaded in Europe and occasionally seen in European rifles, but never loaded or chambered in the United States. The 6.5x52R is extremely similar and visually indistinguishable from the American .25-35, but actual dimensions are slightly different, specifically, 6.5x52R specifications call for a slightly smaller bullet diameter. The two should not be considered interchangeable. Now that Hornady has introduced a .25-35 load modern ammo is available, and .25-35 can be readily handloaded by resizing .30-30 brass. It is best to use .25-35 ammo in .25-35 rifles, and 6.5x52R ammunition in rifles specifically chambered for the 6.5x52R. —
Craig Boddington