Making a spring animation import to Unity

I made an animation with a spring in Blender, using a Stretch constraint. After several hours of Google searches, I’ve learned that constraints aren’t carried over into Unity, but I still haven’t figured out how to make the spring animation carry over. I put keyframes on it, but it doesn’t work. I assume it’s because the Stretch constraint doesn’t appear to affect the loc, rot, or scale.

Picture of the current animation halfway through (note that the spring is supposed to stretch along with the barrel.)

You can only import actions into unity. Create an armature and rig your spring. Then create an armature action to deform the spring. There is a tutorial for a bouncing ball which might help you.