We are an inline shooter, so we have a tube in a tube, and a "truck" that pushes back the "T-bar" and lock a wedge between to fingers that stick out of the end of the pipe. Here is a video when we was debugging the software before we loaded it all the way with surgical tubing still works pretty good with 4 bands (1 band doubled over on each side), about 90 lbs on a fish scale to pull it back and the lock holds it no problem. Small air cylinder to move the wedge out of the way.
http://www.youtube.com/watch?v=Lbv_auENyTM