Cartriges will headspace [bottom out] differently. The first was the rimmed case and the rim would hold the headspace. Later, rimless rifle cases used the shoulder of the bottleneck. Belted magnum rifle cases just move the rim up the case a bit. The acp family of case uses the end of the case to hold the headspace. Yes, that thin wall holds it. If you try a roll crimp or over crimp, an acp it will not bottom and the firing pin may not reach it. Excess headspace that does fire can ruin accuracy or even blow a gun.
