I've never used factory brass in this chambering.
I have both RCBS .280 Remington Dies and RCBS .280 Rem IMP 40 dies.
I start with once fired .30/06 brass, resize with the standard 280 dies to create the false shoulder and then load seat using the IMP dies thereafter. Never had an issue.
My rifle is a Winchester Featherweight XTR in 7x57 which was re-chambered to the Ackley chambering. It is a nice hunting rifle and quite the looker. Best performance from the 22" barrel comes from 140 grain bullets which reach 3200fps with relative ease. Lighter bullets suffer from the shorter barrel and the 175's will hover in the 2800-2850fps range,
