Before the .222 became top dog, the most popular benchrest round was the .219 Wasp, a wildcat based on the .219 Zipper case. Aside from being a rimmed case, it was pretty similar to the .22 PPC, but the trend to using bolt actions (especially the Remington 722) turned the tide in favor of the .222. The .222 is indeed extremely accurate, but the ease of using readily available rimless brass was a big factor, along with the publicity generated by Mike Walker and Remington.
