[RDGAC]

Herewith some photographs of the lock, courtesy the incredibly dimwitted works camera and a lot of patience. I've been test-firing the lock a couple of times, and discovered a couple of points:

1) Having removed, oiled and partly cleaned the cock, it moves smoothly and with a minimum of friction, so far as I can feel.

2) The half-cock notch appears to be both corroded and clogged with god-alone-knows what, but removal of some of this with a small steel pick has not improved results; the sear still grabs the half-cock, and halts the firing movement unless the trigger is kept depressed.

3) If the trigger is depressed, the gun will snap to half-cock and then discharge from there, albeit very quickly - the cock scarcely has time to slow down, but there are two distinct, audible clicks as the sear first releases from the full-cock position and then catches the half-cock notch, so far as I can tell.

No doubt I'm teaching my grandmother to suck eggs, but I hope that the photos show the asymmetrical wear on the tip of the sear itself and the very heavy wear on both the half and full-cock notches. I'm also concerned that the toe of the mainspring is barely being held in place by the tumbler in the "fired" position, which may explain why bringing the gun to the half-cock takes a surprisingly strong pull; certainly much more than the works percussion jezail's lock, which may of course be rather later and is now in better nick.

Edit: And, as promised and somewhat late, the pictures. In order:

1) Lock in full-cock position. 2) Lock in full-cock position, from bottom left and showing wear to notches and sear. 3) As #2 but from bottom of lock. 4) Lock in half-cock position. 5) Lock in fired position. 6) Lock overhead view, showing clearance between cock and plate, fired position.