I have an 8400 and the "bounce" you're referring is quite normal,
@Archer correct me if I'm wrong but I believe what you're feeling is a click spring (or yoke or whatever the hell its called) engaging the barrels (because the movement has two btw) to keep the mainsprings dumping their energy in an uncontrolled way. Keep in mind that although I know the symptom my guess to the cause is a total wag based on my limited experience opening watches. Also, I wouldn't worry too much about the manual winding being "tough", again so long it winds and gives that familiar soft buzzing we all love as our watches come to life I think you're fine. I really believe its because you're winding two mainsprings vs one, my SD and Speedy have less resistance than my Seamaster 300. Again, I'm no expert but I've experienced your observations and I feel its normal.
Congrats and wear it in good health.
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