There is .021" difference in length from the case head and shoulder/neck juncture meaning the 7 Remington mag is the longest and when standing up it is the tallest.
What does all of this mean? If you use the 7 Remington Mag neck sizer on the 280 you have a section of the neck that does not get sized. Some reloaders require theory when a do-nut appears. Some do-nut appears because of bad habits. If you are using a RCBS shell holder you can reduce the upsized portion of the neck by about .010" if you shim the case off of the deck of the shell holder.
F. Guffey