The 7mm TCU is another of the series of cartridges developed by Wes Ugalde for Thompson Center and offered as a standard chambering in the single shot Contender pistol. All are based on the 223 Remington case necked up, this one to 7mm (.284"). The 7mm TCU dates back to 1980, or thereabouts, and has become quite popular for metallic silhouette pistol shooting. It is also known as the 7mm x 223. The 7mm TCU has a reputation for exceptional accuracy and makes a good varmint cartridge in the T/C Contender pistol, particularly with the 14 inch barrel, which provides an extra couple of hundred fps over the 10 inch barrel. It is on the marginal side for deer or other medium game. The originators recommend that only commercial 223 Remington brass be used for forming cases. Don't use military brass. Cases are easy to make and can be formed in one operation once the dies are properly adjusted. Proper case length is 1.740 inches. 

This text is based on information from “Cartridges of the World”, Hodgdon reloading manual, the cartridge designer and/or own resources.