[shotgunworld]

Today the brass portion of the shell (more often brass-colored steel) has a primarily decorative role. All-plastic shells like Cavim, Eclipse and Activ have demonstrated that some compression-formed plastics are quite strong enough for shotshell use with no metal reinforcement (it should be noted that all-paper shells were tried, too). Tall brass is still used on high-powered shells (especially those from Italy), but its purpose is marketing appeal.

source: NRA Fact Book