The cartridges were developed for the Thompson Center Arms Contender single shot pistol, and are widely used in handgun metallic silhouette competition and handgun hunting.
While not as strong as bolt action designs, such as the Remington XP-100, the Contender is capable of handling medium power cartridges, and many wildcats appeared based on cartridges such as the .30-30 Winchester and the .223 Remington.
The larger calibers provide more downrange energy, and resist wind deflection better than the original .22 caliber (5.56mm) bullet, and the moderate case capacity of the .223 Remington works well in the short pistol barrels.
[2] Generally, only new, unfired .223 Remington brass is used for handloading TCU cartridges to avoid the premature case neck splits that can occur when resizing previously-fired .223 Remington brass with TCU reloading dies.
Done this way, TCU sized brass generally becomes as reliable for multiple reloadings as any other handgun cartridge case.