I'm rebarrelling a rifle to .444 Marlin. I just lre-earned that headspacing a rimmed cartridge isn't as easy as I expected.
A rimless cartridge, the distance from the base to the shoulder is fixed within narrow limits at time of manufacture; usually no more than a few thousandths at most. Rimmed cartridges seat on the rim. Cool.
The SAAMI drawing for the .444 cartridge says the rim thickness for the .444 Marlin is .064-.010, or .053-.063. That's a .010" variation between the limits.
.444 GO gauges are .063, and NO-GO are .067; that's .004" maximum headspace.
If I set up for zero headspace on a .063 rim, I should be okay; I've never seen a thicker-than-spec rim on anything. But even with zero headspace on .063, a minimum rim can give me a headspace of .010" - or .014" if I'm on the edge of the NO-GO with the .064".
How likely am I to see thin rims in .444 brass? I ran into this once, years ago, with a .45-70 conversion, with rims all over the place, and wound up standardizing on one brand of brass so I could keep the headspace consistent.