I am still in the parts-gathering process of my .280 AI build, because it will be an unusual project for me. I will be making my 700 into a "switch-barrel" rifle, and I will be using 2 different calibers, .280 AI and .25-06 AI, so I can swap back and forth, since I only have 1 standard bolt-face long-action sitting around. All the rest are magnum long-actions.
Therefore, I don't have any experience loading for that caliber yet...But will keep you informed once I do get things underway.
However, in my other calibers I have gone past book specs on a few, but have found that some books are warm, while other books really like to give you a MAX recommended load. For example, my Nosler 7 book gets you warm...But my Berger manual when it says MAX load, they truly mean, proceed with caution if you go any hotter than this...
Also, different calibers are different. For example, my .308 isn't very picky at all about which loads I put in it. My Rem 7mm STW, Browning 7mm RemMag, and Accumark .257 Wby are VERY
picky, and you have to find the proper node for the barrel.
Seems to me that in my experience, the non-magnum calibers don't seem to be as picky as the magnum calibers are at finding a "sweet-spot" in your load.
Granted, I am far from an expert at anything, I'm just giving my opinoin and my experiences.
So, once I get my .280 AI built, I'll let you know how the load development goes, and how picky it is, or is not.