When I first got my Dasher, the smith recommended the false shoulder method and a bullet. I shot a number of 300 yard matches fire forming Dasher cases from 6BR’s.
The reason he recommended a false shoulder over just a jam was in his opinion, the firing pin impact would move the case forward, ever so slightly, and upon firing would force the case head against the bolt face, potentially stretching the case, weakening that area, which in time could lead to head separation. Whether correct or not, using the false shoulder method has allowed me to reload those cases over a dozen times and still going without a single case failure. Take it for what it is.
However, now it’s just the COW method, still with a false shoulder of course.