Complex sentence: It fired 50 kilogram (110 lb) HE shells, which contained far more explosive filler than ordinary artillery shells of the same caliber because the low muzzle velocity allowed for thinner shell walls and hence more space for filler.
Split into simpler sentences: It fired 50 kilogram (110 lb) HE shells, which contained far more explosive filler than ordinary artillery shells of the same caliber. The low muzzle velocity allowed for thinner shell walls, hence more space for filler.