The impact may have been greatly slowed by water. A difficult medium to penetrate.
I've shot a bit of swagged lead bullets including the Speer product. Not enough at once to have any conclusion about leading as compared to cast. I think the Speer can usually withstand greater velocity than the Hornady one's. I try to keep them for mild loads.
Apparently from what I've read. 357mag brass was scarce way back when. Many scribes of the day including Keith, Skelton, and Taffin loaded 38spl brass to magnum strength for use in magnum revolvers. If I had the brass, I'd be more inclined to download magnum cases for less jump to the rifling.
