There is a wimpy little clip. Anything over 45 grains seems to release it. Most people use a rubber band or strap. Some develop a habit of slapping it back up each time it drops. The originals did this and the reproductions faithfully do this as well.
Does the Walker even have a clip? From pictures I see, the loading lever handle seems to be suspended underneath the barrel and held up by a weak spring tension. The Dragoons have the clip, but they still come loose with stout loads.