Slier & van Keder

Hello, can anybody tell me the origin of the names Slier & van Keder?
They are printed on a 12 ga shotshell made by Eley. Headstamp is Eley 12 ga Gastight.
They sound dutch to me but we know no persons who had anything to do with ammunition in Holland.
Perhaps it is South African??

Any help is welcome
Regards René