It's a converted spring rest. GKF turned the infinity rest into a drop away. I think they just used the same setup but crancked the spring backwards which makes it stay down instead of up. Spot hog nows sells it, but I don't think they have it as a drop away. The spring inside would vibrate at the shot. Dropping the wax inside stopped it and didn't hurt the way it worked.

I had a site once with a long fiber cable wrapped around it. It rattled too. I taped that one but I think the wax would have worked better. Sometimes when I have something that catchs or squeeks I rub a candle on it. I guess my brain just took a leap. Great for putting on a door stike plate when a door won't shut without turning the handle.