I have a bucket on s3, and a user given full access to that bucket.
I can perform an ls command and see the files in the bucket, but downloading them fa
I think you need to make sure that the permissions are applied to objects when moving/copying them between buckets with the "bucket-owner-full-control" acl.
Here are the details about how to do this when moving or copying files as well as retroactively: https://aws.amazon.com/premiumsupport/knowledge-center/s3-bucket-owner-access/
Also, you can read about the various predefined grants here: http://docs.aws.amazon.com/AmazonS3/latest/dev/acl-overview.html#canned-acl