So, would the cart be pushed in, and turned to lock in place...?...Depending on the material, I assume rubber/plastic compound would be fine, and if it is dense enough, it would have vibration reducing properties as well as a solid feel when gripping....Providing, it works with the "available" plungers, or, if the plungers can to be "snipped" to suit, it looks like a viable and interesting addition, as I don't mind adjusting my tube tip to suit my depth/throw.. My only concern would be the material of which it is composed of...Wish you well on this Franco...