You place some joints, go to the joints tab and assign parts to the joints.
Click animation on the bottom, And Press Ctrl+K to set an keyframe.
Go a few frames further on the timeline, change your model, press Ctrl+K again. You can drag the slider or press play to see your animation. When exporting (You need DTS Plus Exporter) Click add under sequences, give it a name like reload, and enter the desired frames.