There are several choices for the spring ball part with all self contained and won’t come out. Some you drill a hole and glue inI really like the set screw with ball if I could find a size that will work.....ie if there is enough room to fit in.
I also think if you just use a steel ball with spring.....the cross pins have to maintain a pressure on the ball to get it to stay in. There is a space difference between a 5 shot and 6 shot speed loader, so that will have to be taken into account.