Firearms/CXP
CXP Guide - http://www.chuckhawks.com/cxp.htm
This number is supposed to be a general guide to the appropriate hunting application (game weight) of the various loads for centerfire rifle cartridges.
Winchester calls these "CXP" classes, from CXP1 through CXP4, and has registered CXP as a trademark. CXP stands for "Controlled eXpansion Performance." Federal lists Usage numbers from 1 through 4 for rifle hunting ammunition. With or without the CXP designation, the numbers 1 through 4 represent the same four basic types of game in both ammunition catalogs.
CXP1 class game is composed of small game, varmints, and small predators that weigh less than 50 pounds. Typical examples would be species like sand rats, rabbits, prairie dogs, woodchucks, and coyotes. These call for bullets that expand very rapidly or fragment on impact. The Hornady V-Max, Remington Power-Lokt, Sierra Varminter, Sierra BlitzKing and Speer TNT bullets are good examples of the type.
CXP2 class game are generally light framed animals with relatively thin skin and light muscles and bones. These are primarily deer, antelope, sheep, goats and black bear. They typically range from about 51 pounds to perhaps 300 pounds. According to the Winchester Ammunition Guide rapid, controlled expansion bullets are best for this class of game. In appropriate calibers the Federal Hi-Shok, Hornady Interlock, Nosler Ballistic Tip, Remington Core-Lokt, Sierra Pro-Hunter and GameKing, Speer Hot-Cor, Swift Sirocco, and Winchester Power Point are proven performers.
CXP3 class game are large framed, heavy animals with tough skin, heavy muscle tissue and large bones. I would guess that these animals range from 301 to over 1000 pounds, and would be represented by such game as alg, elk, moose, zebra, kudu, eland, and brown bear. Bullets should be designed for delayed, controlled expansion and deep penetration. Premium bullets like the Barnes X-Bullet, Nosler Partition, Hornady InterBond, Remington Core-Lokt Ultra, Swift A-Frame, Federal Trophy Bonded Bear Claw, Speer Grand Slam, Winchester Fail Safe and Partition Gold, and Woodleigh Weldcore are often recommended. But in appropriate calibers more traditional designs like the Remington Core-Lokt and Winchester Silvertip have also proven very successful for a great many years.
CXP4 class game are the extra large animals often referred to as thick-skinned game. These are primarily African species like Cape buffalo, hippo, rhino and elephant, but also include such species as Asian and Australian wild water buffalo and American bison. These creatures run from an average weight of about 1000 pounds for Cape buffalo up to 12,000 pounds for African elephant. Calibers from 9.3mm or .375 on up are usually recommended. Expanding bullets for animals this large should be very heavily constructed such as the A-Square Dead Tough, Barnes X-Bullet, Fail Safe, Trophy Bonded Bear Claw, and Weldcore. Solid (non-expanding) types designed for maximum penetration are the traditional choice and are widely used in Africa for thick-skinned game.