Could some thermobaric tow or three satage explosive grenade be made for some old grenade launchers? A thermobaric explosive is a very powerful two or three stage exploding out some proppane or other gas, then igniting it with a secondary explosion

A typical weapon consists of a container packed with a fuel substance, the center of which has a small conventional-explosive "scatter charge". Fuels are chosen on the basis of the exothermicity of their oxidation, ranging from powdered metals, such as aluminum or magnesium, to organic materials, possibly with a self-contained partial oxidant.

thegatalog.com has 3D printing files for stuff like grenade launchers, fully automatic weapons, handguns etc.