Look at the Firenock Aero-Outsert table. Looks like you need a AOA 6.33 for an Easton Carbon Injexion 280.
As a note, I shoot the Carbon Injexion 330 and like the Firenock outsert system alot after 4 or 5 years of use. I put them on with Bohning Hotmelt, being careful not to overheat the shaft. Put a field point in and spin them to get perfect outsert alignment I also put the D-6 insert in for an extra 20 gr of front weight. Reinforces the front of the shaft as well. Good luck!