I used to fireform a 30-06 JDJ (T/C Encore wildcat w a short neck, max case capacity) by seating the bullet hard (jammed) against the lands (as JDJones himself recommends ) and have never had a problem fireforming ammo this way.
I also think you could form 280AI using '06 brass. Case would be a bit short but that in and of itself won't be a "problem".
If you have a tight neck 280AI chamber, it may be best to turn necks after sizing down.
Simply sizing the neck down to form the shoulder in the appropriate spot for getting a snug fit in the chamber will also eliminate case stretch.
Originally Posted by woods
IMO seating the bullet to the lands will not prevent the case from moving forward and taking up all available head clearance and reducing headspace (on the case) to zero and even moving the shoulder back a couple of thousands.
The firing pin strike and the primer going off in the primer pocket will push the case forward with several hundred foot pounds (more than enough to seat the bullet further unless you have one helluva crimp). A false shoulder will mitigate case movement forward but will not totally prevent it.