A .280 remington is the same as a 7mm remington express just the .280 is basically a +P version, you can use a 7mm rem express in a .280 but cant use a .280 in a gun chambered for 7mm rem express for chamber pressure reasons. But anyway a .280 remington uses a .284" diameter bullet which is equal to a 7 mm bullet so basically to help you understand a .280 uses a 7mm bullet. hope this helps you.