Almost certainly Selleir & Bellot solids, I have one in an orange paper hull on my desk as we speak but can no longer find them on the web. Maybe they dropped the solid slug from the "Plastik" range when they actually moved to plastic hulls! Sounds like an oxy-moron (?), but the S&B 'Plastik' range introduced their plastic wad I believe, the orange paper slug-cartridges had a brass-rivetted plastic over-wad on top of the projectile as well.

Here is an S&B "Plastik" cartridge from their current range:

...and this is what their current slug cartridge looks like now:

Hope this helps.