Introduced circa 2019, the 6.5 Weatherby Rebated Precision Magnum (RPM) is one of a short list of modern SAAMI-standardized designs using tight chambering and ammunition tolerances to improve accuracy. Where many recently standardized chamberings continue to use tolerances entirely appropriate to Horse-and-Buggy Era designs, these superior designs utilize entirely feasible tolerances appropriate to the Space Age — it only took 50 years after a man walked on the moon for gun-makers to get there. This round uses what is nothing more-or-less than a lengthened version of the 6.5-284 Norma case, with similarly tight tolerances. As such, it offers significant performance and works well only with very slow burning modern propellants. While I am no great fan of a rebated rim, such as the 6.5mm RPM has, a difference in diameter of only about 0.027-inch between body and rim should not cause any problems with feeding from the magazine of any well-designed gun. I never heard of anyone having functionality problems with the 284 Winchester, which has the same rim and body diameters. With the best modern components, while dispensing with the issues caused by the useless belt of traditional magnums, this more compact round will do anything the older 257 Weatherby Magnum will do. When loaded with the heavier and more efficient bullets available in 6.5 mm, it will do things the 257 Weatherby Magnum can never do.