Light general aviation piston twins have full-feathering props. It's normal to perform feathering checks by pulling the prop level all the way down to feather, briefly, and observing the changes. First, why is the feather check performed and what is the pilot looking for during this check? Also, how far should the RPMs be allowed to drop? Could allowing a large RPM drop cause mechanical damage?
I realize that the specific allowances may vary between Lycoming and Continental engines and between models, but an average number would be helpful for the sake of the question.