I'm still stumped after I got a pic of the chamber casting.
The rim thickness is .050
Rim Diameter is .548
Base Diameter is .494
Case length 2.02
Neck diameter is .46

Lands show .413
Groove is .427
Rim to rifling length 2.6"

It doesn't show any necking down. Just a plain straight walled rimmed cartridge.
HELP!!??!!