This is a box for .357 Magnum cartridges, made in Palencia. Manufactured for the civilian market in several lots over the years.
The propellant is WC-295 ball powder from Olin Corporation.
Brass Berdan primer, green annulus.
Semijacketed flat nose bullet, 8,30 gram (128 grains).
Headstamp: (SB .357).
Reference: Molina-Orea page 960.