The other good thing about .444 Marlin brass is the heavily constructed web at the case-head.
Much thicker brass web than any other cartridge case, period!
Provides a good margin of safety in a rear-locking action, when pushing pressures a bit.

I have been running a poor-man's .375 JDJ in a 1941 Lithgow No.1 Mk.III for about three decades now and it loves the 250gr Sierra SBT.
Makes Group 1 Nitro for Big Game Rifle competition all day long, and has killed a bunch of buffalo.

IMHO the .444 is a great choice for donor brass in the Smellie.