Speer SWC

[BunkTheory]

is the speer 158 grain 357 swc intended to be used with the bottom groove as a crimp groove to create a magnum case capacity?

[Winger Ed.]

Not really.
They're swaged, and the second/lower groove that looks like a lube groove is on it maybe just because
people expect to see one on a Lead .38SWC, and the grooved model would sell better than a slick sided one
with only a top/crimp groove.

Anyway:
Its really intended to be crimped in the top groove in whichever case you put it in.
Doing that, your OAL will be correct for either case.

If you want .357 performance with it,,,,,
I'd sure encourage using .357 brass and using the intended crimp groove.

Also- its real soft. Don't be surprised if you get some leading at .357 speeds.