Your Halifax is basically an R model Darne. But, you have missed an important clue as to the operation of your gun. The part you refer to as a "barrel latch" lies directly under a pretty serious cam that moves in the breech block with the opening lever. If you remove the breech block from your Halifax, you can watch the movement of the cam, up and down, in relation to the position of the opening lever.
The cam, in the closed position, comes down with great leveraged force upon the back part of the spring (it is a tempered spring, by the way, and the two forks at the front are the part most often broken by amatuer gunsmithing on a Darne-if you need a spare, I have a few around, squirreled away from my decade as the importer on visits to the factory) with the pin in the center acting as the fulcrum to force the forks at the front into matching slots in the barrel. This also is an interference fit. It must be broken in order to take the gun down.
V and P model Darnes, and, Charlins, are of a different design than the R, and take down a bit differently.
The springs that drive the strikers are indeed coil springs. These are NOT "main springs" in a Darne R design. The arrangement is somewhat similar to that in a Mauser bolt gun.
Best,
Ted
