HI
Grendel - your technique and explanations are clear and great helpful.
Rowan - can you attach some picture of your scene with claws and its bones visible - it seems to be problem with weight-painting of claws.
Here is .car file with rigged claws so no manual rotation is needed for closing and opening , just move target helper.Sample animation included.Analyse bone rigging and weight-painting. And have a fun.