They don't need much maintenance, or lubrication, for that matter. If a firing spring breaks in a Darne, the correct procedure is to simply shrug and keep shooting. Almost no lubrication is needed.
Illustrated from top, R action block, center view is the very beginning rough action cuts made on an action forging, this is a piece from the late 1950s, and judging from the lack of rust, was likely destined for a magnum gun as it appears the material is XTC, a high chrome tool steel used in that application. Last is a very petite V action with the key pulled out of the center cut.
I've seen a few drop locks and Darnes offered up for sale at a good discount over the years with the problem of locks or sliding breech being missing in action.
Be careful out there.
Best,
Ted
