Mr. Guffey;
If you have a true "zero" clearance chamber- where the boltface pushes the shoulder tight against the shoulder wall- and at the same time there can exist no gap between the casehead and boltface, then obviously it can't be driven forward by the firing pin.
Most chambers are not like that, with the case pushed tightly against the chamber shoulder threre is a gap of a couple of thousandths or so between the boltface and casehead. In this situation, simply pushing the case into the chamber does NOT seat the case as far forward-tightly- as it can go.
The FP does indeed take up the slack of those thousandths prior to primer detonation.
Not going to debate the point further...
If you have a true "zero" clearance chamber- where the boltface pushes the shoulder tight against the shoulder wall- and at the same time there can exist no gap between the casehead and boltface, then obviously it can't be driven forward by the firing pin.
Most chambers are not like that, with the case pushed tightly against the chamber shoulder threre is a gap of a couple of thousandths or so between the boltface and casehead. In this situation, simply pushing the case into the chamber does NOT seat the case as far forward-tightly- as it can go.
The FP does indeed take up the slack of those thousandths prior to primer detonation.
Not going to debate the point further...