I would not alter the die in any way, shape ,or manner.
It has been stated that you will void your warranty ,which of course you will.
In the aforementioned light. I would send three case samples to Redding for analysis. However the first thig that I would do is to call and ask to speak with any one of there technicians describing your problem., as they are all wonderful problem solvers ( at least anytime in the past I've had any questions or issiues they have always talked me through it ) I am also assuming that you have correctly annealed your brass shell cases beforehand.
Additionally before you return you die set to Redding I would remove the insides from your FL resizing die (You did not state whether or not you are using an expander ,or bushing style of die) and thoroughly clean and degrease this Fl die body as well as its components.
Please note if you find any brass or steel shavings and remove them noting the location and see if they line up with your dimpled brass case shoulders.
(Judging from the image that you submitted they appear to be in approximately the same location) If possible you may want to use an ultrasonic cleaning machine to remove any residual shavings /chips left from the factory. It doesn't take much to to create a dimple in soft brass ,however the real danger would be to Gaul the sizing die body at the shoulder and neck juncture creating a deep grove or scratch in the die itself which if left unchecked will result in a useless die unless you can polish it out under power.
So please examine your die closely for any foreign material and as I have already stated you must anneal your brass as work hardened brass can also yield similar results.
You must rule out everything and anything one step at a time.
Hope this helps ya out or at that the very least will give you something to think about !
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