Adrie,
I'll take a swing at this???
the sear system, to me?, is a two part affair. The lever that engages the tumbler is what I would call the primary and the release is a secondary.
when the cock is pulled to the rear, the primary sear moves clockwise,< looking at it from the inside>. as its nose goes up the tail lowers and allows the secondary to move forward and engage. when in position the secondary sear hold the primary into engagement with the tumbler.
since the secondary sear/release must move backwards.. a trigger bar, pinned higher in the mortise is required. The long bar, situated in front
of the release arm , will cam backwards as the trigger is pulled to the rear. once the secondary moves off the primary, normal function occurs..
Respect Always
Metalshaper/Jonathan