Nice, I used to be a weapon animator at Ubisoft back in the days ;D
Animated maybe half of all FarCry 3 weapons :-)
Simple animation principle apply to this as character animation:
Did my key poses & major breakdown (no timing)
Move them to get proper timing
Spline and secondary breakdown
Tiny detail I love seeing in this: the injection site wounds
idk how often I watch games with injectors just completely forget to include puncture wounds, so it's nice to see them there