Half-Life 2 Cut AR1 (AK) Original Animations
The AR1 was a weapon from the early development era of HL2 that was cut in the final release. By the time the game was leaked in 2003 there were no animations for the model left in the game.
In the 2023 Valve Repo Leak the source files of many models and textures were found including some from Half-Life 2. Among them were model files of the AR1 including its original animations.
Considering it was already in the process of being removed in the HL2 Leak and that the style of model, textures and animation is very reminiscent of HL1, it can be assumed that it was created very early in HL2's development.
Note: The magazine rigging was bugged in the original files and sadly doesn't animate properly in this video.