2 pound block of Roma Plastilina Modeling Clay. This has been used by special Effects people for years to back up and direct the force of pyrotechnic squibs. Hard at room temperature, when heated is easy to mould. Want to have a flat squib blow a hole through balsa wood? Tamp it with a wad of plastilina and the force of the squib will be directed through the breakaway. Kind of "Old School", but it is a useful tool.