A tie. Because the two rounds are so popular, everyone loads for them, and there’s a whopping choice of bullets. The 7mm Magnum is somewhat more expensive, but the difference won’t break you. As far as bullets by themselves are concerned, the 7mm has a big advantage. The .277 diameter that Winchester thought up a long time ago is something of an odd duck, and has never been used for match shooting. Seven millimeter, however, is one of the most popular sizes, and there’s plenty of 7mm rifles that are used in competition, so there are oodles of target-grade bullets out there, including some that can be used for hunting. The practical range of bullet weights for the .270 runs from 130 to 150, and that’s about it. For the 7mm, it goes from 140 grains to 175 grains, with all sorts of stops in between.