>>9898473You'd have to increase it to SEVERAL TIMES the rider's body weight in order to arrest this .50 BMG monster to reasonable levels if the only measure you're taking is added weight. It's NOT like adding weight to a rifle to arrest recoil - it'll take WAAAAY more than that.
The most effective way to make this device be, well, survivable, would be to switch to a less energetic caliber. You should keep in mind that, if the stic/k/ maintains some elastic spring (or closed gas piston) mechanism as well like that seen with a conventional pogo stick (only far heavier-duty) in addition to the auxiliary power piston, then addititonal energy and altitude could be built up over several repeated bounces/shots. In fact, this is how pogo sticks work in the first place - they allow the rider to add incrementally more energy with each bounce with their legs until the stick runs out of stroke and cannot store any more energy.
So, let's look at a 9mm-powered stic/k/ (again, presuming 75kg weight):
600 J of energy per bounce/shot
Height from one shot: 0.82m = 32 inches
Average force due to shot over 1m stroke: 600 N = 135 lbs
Keep in mind that these energies, heights and forces are ADDED ON to whatever forces are already present due to the spring compression from the last jump. Presuming the rider could hang on for the ride, a 9mm-powered stic/k/ with a 17-round staggered magazine could still reach 13.9 m, or 45 feet before running out of ammunition. IMO, this is more than enough, and it's much more manageable of a ride than our .50 BMG widowmaker.