An addendum, if I may:
The Halifax gun that I own at the moment, and the R10 that has been restocked to fit me, have slightly different designs, and the position of the lever is different, at the point either gun will trip the sears just before final closing. While this sounds scary, lockup in either design is actually complete just prior to final closing. What IS scary, is knowing there IS a difference, to me, anyway. Perhaps this difference is to be expected, as there is most of 50 years between the dates they were produced, and there are "improvements", cost cutting measures, mostly, made to the design of the R10. The first sliding breech guns began leaving the shop in perhaps 1877, and, they are likely still in reduced production now.
That, is a long time. It would be hard to know all the changes to the guns that occured over those years.
I would suggest a great deal of common sense and safety be used when handling any firearm.
Again, I suggest that in the event a live round is stuck in the chamber of ANY design of gun, a different method than tripping the ejectors be used to remove it.
I find this discussion, at this point, to be about as useful as one that would involve how to go about holding the top lever over just far enough to take a conventional double out of battery, and attempting to get the ejectors to trip without doing the same to the sears.
Best,
Ted
