Could be some glue residue inside the point ferrules that cause the little bit of wiggle. If the adaptors fit all the way into the ferrule, they should not wiggle. If they're too long, may need to clip them off or go to a shorter adaptor. I think they'll work though.
5/16 adaptors provide another advantage if used on 5/16 inch shafts and 11/32 broad head ferrules. The broad head ferrule will encase the leading edge of the arrow shaft, making it just about impossible to mushroom the shaft on hits on things like rocks and trees.