Miller,
I believe your method may be flawed. The ejector hook is set just before the shot, and will grab the spent cartridge perfectly, as the shot has molded the base to the hook and chamber of the gun.
Using a spent cartridge from a different gun does not allow that to happen.
I've never heard of a Darne that had extraction issues, at least not extraction issues that were the result of a round being fired in it's own chamber.
It is better to cycle the action briskly, although I often don't, as I prefer to catch the spent rounds on the action flats, rather than letting them hit the ground, and then doing so.
A bit lazy that way, I guess.

Best,
Ted