How else do they form cases? I think the confusion is that the term improved is often automatically associated with the name Ackley. PO designed his improved chambers with the thought of being able to safely fire standard ammo in them, many others didn't. It's not the case that's the concern with the JRS...it's standard ammo. I've never used anything but 270 brass in my 280AI so the shoulder moves forward ~.050" on the first firing. Put a false shoulder on the brass to keep the case head snug against the bolt face and then shoot it. Others use a bullet with a significant jam into the rifling to do the same, I haven't had as much luck with this method. Gibbs rounds move the shoulder forward ~.200" and it's not a problem when done correctly.