A method of synthesising an organic high explosive includes the steps of i) providing a first solution A, ii) providing a second solution B, wherein the admixture of solution A and solution B are selected such that they are capable upon formation of the admixture of reacting together to provide an organic high explosive, and iii) causing the solution A and B to be mixed and passed through a flow reactor to create an admixture, wherein the flow reactor includes a pipe, wherein the internal diameter of the pipe is selected such that it is less than the critical diameter of the organic high explosive, thereby preventing detonation of the formed organic high explosive in said flow reactor.

This specification discloses a continuous flow reactor comprising a reaction vessel enclosing a rotating shaft which bears multiple impellers. A removable insert comprising baffles separates the interior of the reaction vessel into multiple interconnected chambers each enclosing at least one impeller, and a gap between the outer edge of the baffle and the vessel's interior wall facilitates insert removal for maintenance but avoids excessive backmixing.