I kept the basic concept but re-dimensioned all the parts for a tighter fit. It now traps the rival rounds well so that they should never fall out of the device when not intended. On the downside it may deform the rival rounds slightly as it is used, but I've never had a problem with this.

The end cap has been simplified (it's only job is to fit on the end of the tube).

The head of the plunger is contoured to better trap the rival round as it is pressed down.

Plunger fits inside the tube with very little slop.

Used in many nerf battles with the Kronos and it has served me well.

Included my design files from sketchup in case anyone wants to further fine-tune the dimensions or make further changes. I know most designers today use fusion 360 but maybe they can be imported? Note the file "nerf kronos speedloader 2 b.skp" is not an actual printable part, it was the starting point to test fit and then extrude the rest of the design from.