A positive displacement explosive base dosing pump is provided with a drive motor 14 and has an outlet 22 connected via a flexible hose 24 to a lance 70. The lance 70 has a mixing device 72 therein and a reciprocable positive displacement gassing solution dosing pump has an outlet connected via a flexible conduit 54 to the lance and feeding into the lance upstream of the mixing device 72. The invention involves using the base dosing pump 12 to pump explosive base from a supply 78 along the hose 24 to the lance 70 while the gassing solution dosing pump 16 simultaneously pumps gassing solution from a supply 56 along the flexible conduit 54. The conduit 54 leads the solution into the lance 70 upstream of the mixing device 72 whereby the explosive base is mixed with the solution, so that a mixture issues from the lance 70 which becomes sensitized after reaction has taken place between the base and solution.