This is a vid I made to show what tuned flopper looks like. The premise of a tuned flopper is that it will open easily to a certain point, then once pulled open further it will not close again on its own.
The first part shows that the flopper will open slightly from it's own weight and close easily as it should when the spear leaves the gun. Upon impact with a fish the flopper will open to the sticking point. Then when the fish pulls on it the flopper will open to the maximum position where vibrations from the struggling fish will not close it.