If you've only loaded one round of each, I wouldn't worry too much about it. If you loaded 3-5 rounds at each weight, and the average of the 43gr load is 100fps less, then, stop. You might not have enough crimp. Is it a taper, or roll crimp FCD?
If its taper crimp, then, try using the roll crimp feature on your regular die. In a separate step.
I love the FCD for certain things, but, there's no substitute for a heavy roll crimp.