If it is properly tuned, then fast or slow shouldn't matter. But, minor issues are often overcome with fast cycling and in general aren't an actual issue.Something that I know about these rifles is that this lever action doesn't like to be functioned slowly. When I offer mine over to new/unfamiliar shooters, we're always tossing and shaking the rifle around to get the cartridge to feed because they like to look in there and watch everything happen. I tell them to rack it like you mean it. No more problems.
If you rack'em in fast, does it happen?
Yes, the tuning never seems to be the same and is the frustrating part of owning one. I have suffered with the Marlin jam. Fixed for now.As for the OP, how is it jamming? You say it isn't going in straight. Is the cartridge going into the chamber at an angle sideways and jamming up? If so, that's an extractor issue.