It's not actually a 280 AI but close enough to get the idea . The deal is the bbl is a simple nominal 277x284 7mm bbl, except the 1st 1.5 inches. The best thing I can do for it would be to send it to a smith and set the bbl back a thread or 2 and rechamber it to a correct AI and eliminate the years of full tilt jacketed shooting.
The fired neck is 299 id and presents a fluid taper to the 27th 28 bbl 1 inch ahead of the case mouth . I have a couple of heavies a 7mm-168 is 1 that will patch to meet the needs or be very close.
I've thought this to death because of components on handrather than shooting the problem out . The neck is the fly , sota-speak, in this 1. I've worked out an 8x39 but it had a 305 x 3165 bbl.
I guess I just don't know if I should go fat paper or fat core at this point. I will probably have the rechamber done anyway but if I can get it started right I'd put it off.