The "daylight" method, noted by Gil, above, is the correct form when using the opening lever as a safety on an R model Darne. There is a position, just between daylight, and the breech contacting the ends of the barrels, where it is possible to trip the ejectors, without tripping the sears. Let me post, here and now, again, that this endeavor always scares the pee out of me, because just a bit further on the lever, and the gun will fire, with recoil closing the action against your thumb. I don't do it, as I have never needed the ejectors to haul live rounds out of a chamber, but, it can be done. Foolish move, as far as I am concerned.
The V safety, and, lever, are a different kettle of fish, few posting here will ever need instructions on the correct use and etiquette of a V model, and at the risk of creating confusion in the unfamiliar, I will post that somewhere else, on a different day, should it be needed.
You guys with a Charlin have no doubt already figured out there is an interrupter built into the mechanism, that prevents firing if the breech is open in the least.
None of this applies to you.
Hard as it is to believe, all three of these versions of the sliding breech gun are completely different, with no common parts, and subtle differences in operation.

Best,
Ted