The nice thing about an Ackley, Is that you can use the factory ammo to do the brake in and if it is set up with the traditional .004 thousandths compression fit, It can also have good hunting accuracy saving separate fire forming.
Even though you may want to use heavy bullets, I recommend using the 140 grain Remington loads for fire forming. (They do a great job of forming the brass to your chamber and are easy on the brass).
If your rifle was head spaced with the standard 280 head space gauge, you will have no problems. If it was head spaced with the new SAMME gauge, it may have to much head space and you will have to shoot factory loaded 280 AI ammo from the first. (It is slightly longer).
J E CUSTOM