The .243 Winchester Super Short Magnum is a fairly new rifle cartridge that was introduced in 2003. It is high velocity round based on design philosophies that should impart a high level of accuracyhttp://www.browning.com/products/features/detail.asp?ID=2 Browning WSSM info. The .243 WSSM is an addition to the WSSM line that also include the 223 WSSM and 25 WSSM.