There's this myth that people don't have adequate strength gripping between their thumb and the forefinger to grab the slide and apply force. Maybe if they're using the fingertips, but humans generally have a LOT of gripping force between their thumb and the side of their index finger's proximal phalanx or interphalangial joint.
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If people without terrible arthritis or another disability are having a hard time racking with a slingshot method, it is nearly always because they are
holding back. They are afraid that they are going to damage the gun, or that the sharp-ish edges of the gun is going to cut their hand. If you can open a water bottle, you have enough gripping strength to hang onto the slide and apply enough force to compress the recoil spring.