Here is how I ended up "fixing" this. I didn't go the route of replacing the coil, even when I found something weaker, I didn't want to have to deal with that being too weak etc.
At the end of the day, I determined that the best way to take some power off the VUK was to "shorten" the length of the plunger. I wrapped about 20 layers of insulated tape around the coil stop. With the plunger up a little higher, it won't hit the ball with as much force.
While to me the ball seemed to be kicked up at the same velocity, it took just enough force off of it so that 10 out of 10 times it didn't hop off the habitrail and it loaded the cannon correctly.
The tape shouldn't wear, the plunger is only coming down with as much force as the spring gives it.
I just didn't like the idea of modifying anything ball touches. Insulated tape, with the force of the ball hitting it, seems like it could wear. And, other means of something directly slowing the ball down just doesn't seem ideal to me.
Anyway, my two cents, and in my opinion, the best, simplest, and easiest way to deal with this issue.