Those look like Berry's hollow base copper plated lead bullets. Copper plated bullets fall somewhere between hard cast and jacketed bullets when it comes to reloading, I'd recommend using hard cast data. The idea of the hollow base is the same as with 38 Special HBWC ammo, the combustion pressure forces the base outward so as to make it better conform to the lands and grooves in the barrel. The end result is improved accuracy.
With these plated bullets come some restrictions on velocity. Exceed the manufacturer's recommended maximum velocity can result in the plating being stripped from the lead, resulting in poor accuracy and lead build up in the barrel.