A little bit of "AI-spice" makes everything nice...
If I was building a .280, there's only 1 way to go.....Ackley Improved 40* shoulder SAAMI spec chamber, so you can load and shoot the Nosler 280 AI brass.
Yes, and no...On the fire-forming question. There are 2 different chambers. There is the original Parker Otto "PO" Ackley chamber...In which you CAN shoot regualr .280 Rem ammo in and it will properly fire-form.
And there's the newer Nosler/SAAMI spec chamber, in which case it is .014" shorter than the orginal Ackley chamber. So you will either have to put your .280 brass through a new die-set that is cut to SAAMI spec to match your chamber, or you can just buy the Nosler .280 AI brass, and load your own from scratch (which is what I would do, because it's better brass than Rem UMC brass is).
So, if I were building a .280 AI (which I have one in the works, just waiting on cash to order my barrel blank), I would go with a new PTG reamer: http://www.midwayusa.com/product/557...egree-shoulder
and a new set of RCBS dies: http://www.midwayusa.com/product/557...egree-shoulder
and some new Nosler .280 AI brass: http://www.midwayusa.com/product/128...lder-box-of-50
and pick your bullets, powder, and primers of choice, and have some fun.