The UK's Finest Independent Forum for Shooters and Gun Owners. Est 2010.

It does sound like the necks have work hardened and are not retaining the resizing from the die and springing back. I think annealing is the only way forward. I have noticed this with .308 PPU cases, but since I don't anneal, at the moment, I use a slightly smaller bushing die. I then run a Sinclair carbide internal neck sizing die through which is 0.002" smaller than the bullet - in this case .306". I find this gives a constant neck tension as the inside of the neck is reformed to a constant, so overcomes any differences in case neck thickness. I am sure this adds to the work hardening effect, hence why I am going to have to start annealing, but pressure for bullet seating is constant and measurements of internal neck dimensions are repeated. In any event to maintain the same neck tension from case to case it is necessary to reform the internal part of the neck and not just rely on the external neck resizing die as I find the brass thickness in the neck of fired PPU cases can vary up to 0.004" on the same case. I mostly use Lapua brass which seem to stay softer for longer. Having said that even my Lapua brass is work hardening to a point that they need to be annealed.