He's talking about the type of HE used in the shells. This saw some development during the war, with the cyclonite family (which included Hexogen and the British RDX) being about 50% more powerful than TNT.
The Luftwaffe seem eventually to have settled on HA.41, which was 80% cyclonite and 20% aluminium, or a Hexogen/aluminium/Montan wax mixture. The aluminium added brisance (shattering effect) plus increased the incendiary effect, the wax was a stabiliser.
Tony Williams: Military gun and ammunition
website and discussion
forum