Now is there an upper weight limit?
Yes there is, I can't remember what it was for the MB Mk 10 that strapped to my backside on the only occasion that I ever flew in a fast jet, but what I do know is that I was only just under the maximum weight and leg measurement limits by a couple of ounces for the former and a couple of millimeters for the later. The primary reason for the weight limits on the older MB seats is to do with the pitch control unit that sets the angle of the rocket motor under the seat so that its thrust angle goes through the centro of gravity of the seat and its occupant. Minimum weight also has an effect of the operation of the parachute, apparently.