Got to the range yesterday and had mixed results with the 280 Ross.
Firstly, the rifle itself was quite well-mannered and a joy to shoot, offering decent velocities for the AR2209 (H4350) loads I tested:
50gr = 2460fps with the 160gr Woodleigh.
52gr = 2590fps
53gr = 2640fps

They say you never stop learning, and at that point I was reminded of the need to check headspace after such radical case-forming, and to use brand new cases rather than once-fired! A couple of primers were high and velocities erratic in the next lot, and one case showed signs of incipient head separation so I bailed at that point.

Lesson learned: don't try radical fire-forming while working up loads at the same time!

The next lot will be brand new cases properly sized for a very light crush-fit in the chamber, and fire-formed with light loads before any further load development occurs.

Will continue this in the Reloading forum when I have more range results to report.
Rained all day today though....