Neat idea. A bit of effort, but that is what you do to make do.
I saw somewhere how to swage the 209 pocket a little tighter to take the 57s. Seems like a steel ball/bearing was used, maybe 5/8"d or so. It only diminishes the opening of the pocket, not the entire depth of course, but supposedly the hull could be reloaded again w/a 57.
I've never tried it.
I have used them occasionally in berdan primed rifle brass,,open up the case for the 57 primer. Low pressure loads only of course. 8x56R was a popular use even after boxer primed brass became available. All that long gone now.
The last 2 bricks of 57 primers I bought were $8 each. Even then I felt cheated,,one of the trays had a couple missing!
