to get an indoor training load( for could winter days) try .25 airgun pellets. the better ones like H&N baracuda, I think they weight around 43 grains.
decades ago I load 25 acp for a guy and, iirc, testloads with the airgun pellet were able to cycle the baby browning.
think I still have a rcbs 25 acp bullet sizer lie around somewhere but there are probably very few who make cast bullets for this caliber.

its an absolute nice little toy gun but what to us it for? very hot load and rabbits