I once had a Kreighoff insert for .22LR in 16ga in a hammer drilling. It had the little pin with extractor notch as stated & also a screw in one side which had a little c'bore cut into the rim seat for the 16ga rim. As Vol said you moved the two little pads around till it would shoot to the sights. At this point you could back off the screw with the key, remove & turn back in to the same setting. I no longer have the insert & forget exactly how it was done, but you then set a stop on the removal screw so it always went back to the same tension. Mine was very accurate & repeted with consistency, but I foolishly let another gentleman talk me out of it one day. I did turn a fairly nice profit on it though.
