There are two main products described as Winchester Super-X Magnum Rimfire Ammunition. As part of the Super-X line, they are able to offer proven dependability and accuracy via high quality and sure functioning, leaving you with a high-performance bullet. Both of the .22 Winchester Magnum ammunition choices are 40 grain and ideal for small game and varmints. The difference is the option of a full metal jacket or a JHP style. The full metal jacket, for example, has 324 foot-pounds of muzzle energy for 1,910 feet per second muzzle velocity.