The MP-412 REX is a Russian double-action .357 Magnum revolver with a break-action chamber and an automatic ejector. It was designed for export (REX, Revolver for EXport), but never put into full production due to lack of a market. The weapon was designed by IZHMECH, the state-owned Russian Izhevsk Mechanical Plant, which also designed and produced the Makarov PM semi-automatic pistol.
The MP412 was unique in that it had a break-open frame rather than a swing-out cylinder design of most modern revolvers and a composite bottom frame consisting of steel with a polymer envelope. The REX never entered full production, possibly due to lack of market interest. This may be due to the break-action design being seen as not as strong as the more modern swing-out cylinder design which is inherently stronger, having a solid top instead of a top latch.