On my old British Enfield rifles I use a trick a Canadian taught me because the headspace on these old rifle can be quite "long".

It's a rimmed cartridge so I just slip a small rubber o-ring over the case and this holds the case hard against the bolt face for fireforming.



After fireforming you neck size only and let the rimmed case headspace on the shoulder instead of the rim.



Using a light to mid range load, .312 pistol bullets and the o-ring I fireform the cases.