I have recently had a problem with fireformed 280AI remington cases developing a head seperation crack on the first firing after fireforming. One case actually split in two. I took the rifle to my gunsmith who found that the bolt closed easily on the 280AI no go guage with some slop. He felt the rifle is unsafe because the fireforming process has to stretch the brass too much thinning the case in the web area. I am not sure about this.

Well I have numerous wildcats where the shoulder has been moved forward so that factory brass would not headspace. Sounds to me like who ever chambered your rifle for a 280AI either took a 280 Rem and improved it without setting back the barrel one turn. Or simply ran the reamer in a little deep. If it were mine I would form the brass differently. Either necking it up to 30cal and then back down forming a false shoulder that gives you a crush fit. Or by setting the bullet into the lands. When you resize the brass set your die so that the shoulder is not set back. I would simply not use factory 280 rem ammo in it.

yep,...sounds as though the chamber is incorrect. Seat the bullet deep in the lands and use a charge of fast powder that is right in the mid-range. If the chamber is correctly done,..you should be able to take a new peice of brass,..insert it with no bullet or primer,.just the case,..and when the bolt closes you should feel the .002" crush of the shoulder against the chamber. If not,..it is more than likely oversized/incorrect.

I would take that rifle back to whoever sold it to you and ask for a refund or have whoever did it fix it.

It just seems like a problem that will never go away so get it fixed one way or another.