The headstamp SB, associated normally to the Pirotecnia di Bologna in 6.5x52 ammo production, actually stands for SIGMA, Societa’ Italiana per Granate, Munizioni ed Armi ( Company for Shells, Cartridges and Weapons), founded in 1917 by one Bondi, a reckless entrepreneur who had already set up the successful
ILVA steelworks at Trapani, southern Italy, where there was a large Italian Naval Base.
He set up in a disused area outside Bologna and through his Ministerial connections acquired a large contract to supply P di Bologna with Fuzes for shells, and millions of sets of cartridge cases and projectiles for the 6.5x52. He also got the recognition of Official Supplier to Military Industry.
With the end of the war , in early 1919, the factories were closed, the machinery relocated to other Govt. Plants, and the land and buildings sold to the Officine di
Casaralta, a post war company dedicated to manufacture and repair of railway rolling stock; skilled workers were absorbed from the 8,000-10,000 Munitions workers laid off from P.di Bologna and SIGMA.
Info from Italian Annual History web site dealing with Bologna from 1796 to today.
BTW…I think SIGMA also made chargers as well.