Just locked up the loading shack pondering the latest mystery. What the heck kind of brass is that?
About 25 of them from the "miscellaneous to-do" box were plainly head stamped as .257 Roberts from Remington and Winchester. They refused to chamber after sizing. Another dozen Winchesters, stamped "W-W Super" worked fine. I didn't feel like pulling the data sheets and getting out the mike, but I suspect I might have a couple dozen "improved" cases.
Minimal rechambering was a popular project for few decades just after World War 2. The usual goal was to increase case capacity by reducing taper and sharpening the shoulder of a standard caliber. The big attraction was the ease of making the improved cases. You just fired a factory round in the altered chamber and, presto, you had your "improved" brass. They called it "fire forming" or "blowing out."
P.O. Ackley was the Improvement Godfather, and he was candid in admitting that some of his (and other's) wildcats weren't worth the bother. How much trouble do you want to go to for for an extra couple hundred feet per second?
But it's fun to own a handful of "improved" cases for a caliber already steeped in nostalgia. Makes a guy feel all fuzzy and retro. I will not, repeat not, even think about acquiring an improved .257 to fit the odd cases. At most I'll give them some warm milk and a soft place to sleep.
All the .223 McNamara Stalemate is ready to prime. There were fewer than estimated, just over 300, enough to feed a mere ten magazines of the proper size. Maybe I can hustle some more at the local loophole.