An improved support for a seal is provided in the form of a back-up ring that reduces or eliminates the gaps between a pump plunger and a high pressure cylinder of a pump. The support includes a back-up ring having opposed first and second faces with a wall thickness disposed between the faces. The back-up ring includes a frustro-conical concave surface on the first face and a frustro-conical convex surface on the second face. Also provided are a packing assembly including at least one back-up ring and a reciprocating pump incorporating the at least one back-up ring.