Of the multiple Winchester 101's that I have or had, this is the only one I know of having this feature.

If the hook is an anti-doubling mechanism (like I suggested above) or a feature to prevent accidental discharges if the gun is closed hard, it seems to me like a "rube goldberg" solution to a poor trigger design? But, the 101's were not known for bad tirggers, at least as far as I know.

. . . just thinking out loud . . .

--shinbone