As I recall, a few years back Savage noticed that they were getting rifles back with stretched chambers in the WSMs and similar fat cartridges so they came up with the "large shank" concept to add some meat to the barrel to handle these cartridges. Check out the Savage firearms list on their website and you will note that when you order a 300 WSM or similar you get a large shank action/barrel. The 28 Nosler is similarly a fatter cartridge though longer than the WSM so they to - if Savage offered them would be in a large shank. Having said all of that, I've got a 300 RUM in a small shank and had no problems but... if I were going new with a 28 Nosler, I'd go large shank.