Yes, those are .22 BB caps (aka 6mm Flobert, invented in 1845 by Louis-Nicolas Flobert but originally produced with a conical pointed bullet and then with a round ball). They were specifically designed for indoor target shooting. A round lead ball with no powder, just a primer, so very quiet and low velocity. The acorn headstamp is for the German company RWS (Rheinisch-Westfälische Sprengstoff Fabriken) but they have used it for a long time, so their cartridges are difficult to date.
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