Higher grade Westleys had spring loaded sight blades which helped to keep them in either the down or up positions.
The sight base was hollowed out and a flat spring, I would guess bent in a wave form to meet each blade pivot from the underside, kept pressure upon the blade. I envision each blade having little flats 90deg. to each other but I would have to see one apart to know for sure.
Really, quite a simple design and a wonder that all rifles with multiple sights didn't incorporate something similar.
Especially if intended for dangerous game use.