Thread: Need help understanding shoulder bump

I got a set of the Hornady headspace gauges, from what i've read online the D 4.20' one should suit the shoulder, but it doesn't seem to give a snug fit and is hard to get a reading off as it wobbles a bit. Does the expander ball in the neck sizing and FL sizing Redding dies function the same way? It looks like Lee don't make a collet neck die for the .338, I'm wondering if there is any advantage of using a Redding neck size plus body size dies, versus a Redding FL size die if they are set up the same for minimal shoulder bump?
Cheers, Tom