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If I were you I'd leave the 3-5 fired cases for now, they probably need annealing so may be giving you measurement issues.

Shoot the 20 new pieces of brass and measure them all after on firing...

FL sizing and bumping the shoulder is the same thing, bumping the shoulder the method of trying to work the brass as little as possible, rather than sizing it back to Sammi specs which would be...

If the die is sitting too high off the shell holder then you aren't even touching the shoulder.

I assume you are trying to bump the shoulder 2 thou not 20 thou?
Bumping more than .002" is...