If they're opaque (can't see through them) they could be old Activ shotgun shells. The company that makes Kent bought the plant that Activ used in W. Va. These shells were completely smooth plastic, save, of course, for the primer. The 12ga. shells were brick red. Supposedly good shells, Activs didn't sell well 'cause they looked, well... cheap. I haven't seen these Activ shells for about 12 - 13 yrs.
I'm the guy your Mother Goose warned you about.