HI, this is my speedloader 'system' for Nerf Rival Kronos. You need to replaced the 'flap' with this parts. It allows you to load rounds without needing to flip open the flap and also make loading easier as you can drop 1-2 rounds in and then push them into the internal mag.

To make loading much faster, you can also print the tube part which can fit 5 rounds (ignore the one in the picture, it is shorter). To load into the Kronos, simply plugged into the hole on the flap and push all the rounds in (priming pulled back of course).

UPDATE: New tube part. Not too tight on the round and allows better rounds loading into the Kronos

UPDATE: I made some adjustment to part 1 (the flap), moving the hole further back to make it in line with the internal mag for smoother loading.