I finished my slingshot.
I used shock-cord, gorilla tape, my Yamaha Heavy Duty Pocket Driver with a 1/8" drill bit, and the Rebar.
For the pouch, I used a 3.5" piece of gorilla tape tripled over. I made holes with the reamer. I cut two 30" pieces of shock-cord, which attached to the pouch with a lark's head knot. I drilled two holes in each arm, threaded the cord through, and tied friendship knots. Some minor adjustments to get the two shock-cord loops the same length, to have the pouch in the middle, and it is ready. I have very few steel ball bearings, so I'll have to buy more, or just find small round-ish pebbles, or use glass marbles.
-This was tons of fun.
-My pouch should be 4" to allow larger projectiles.
-The two holes for the shock-cord should have been closer to each other.
-I used shock-cord loops to get two lengths on each arm, for more stability, since I did not use flat bands.
-If you go this route, drill holes that match the shock-cord. Too big holes, and you'll get too much clearance. 1/8" holes for mine are perfect.
-Drill the holes carefully, at the right angle and orientation, and running parallel to each other. Go slow.
-Cut longer bands than you need. You can always make it shorter and trim it down.
-If you make the pouch/seat out of Gorilla tape, do not use too many layers. You do not want it too stiff.
-I tripled over the gorilla tape while having it on a table. When it was finished, it sat flat, so when I bend it to house a projectile, it makes a crease in the middle. When making a gorilla tape pouch, make it by curving the tape around a bottle or another cylindrical object, so that when the pouch sits idle, it is naturally curved.
-Do not make the pouch holes too big. It will unnecessarily weaken the pouch when you draw.
-Do not make the holes in the pouch too close to the edge. The bands may rip through it.
-When removing the bark, the grip will become slightly narrower. Use a Y branch that fits your hand, or that is a little larger. Remove the bark and just sand it down until you are comfortable holding it.
-When you first test it, make sure you have tied the bands and pouch properly, and wear eye protection.