Determining Fit
Let’s define “fit.” Can we reach all the parts we need to manipulate without shifting our grasp? Can we get enough hand around the girth of the grip for a solid hold, but still have room for the support hand — without our hits or speed suffering when shooting one-hand-only? For good shooting, trigger control is the heart of the beast which makes trigger reach a key factor in fit. On the gun, it’s measured from the point at the center of the backstrap where the web of the hand rests, to the center of the face of the trigger.
On the hand, it’s measured from the center of the web of the hand in line with the long bones of the forearm to the chosen point of contact for the finger on the trigger. Depending on the gun and the shooter, it might be the “pad” of the finger (think, “the whorl of the fingerprint”) or the distal joint on the palmar surface the old-time double action revolver shooters call “the power crease.” I have learned to live with either (and have to, on GLOCKs or the first shot from a Beretta 92), but prefer the power crease because it gives me more leverage.