Of the several critical aspects of getting a handgun to do what you need it to do, when you need to use it, the grip has to be one of the most significant. Properly indexing the handgun to the desired point of aim / impact, naturally positioning the weapon's controls (trigger, safeties, and releases), and compensating for recoil to provide correct cycling, user control, and comfort readily come to mind.
When fitting the handgun to a prospective user/owner, the most important consideration is always trigger reach. If the gun in the hand has too long, or too short, a trigger reach, it is going to b e difficult for the user to handle the handgun properly or shoot it accurately. Trigger reach is measured on the handgun by measuring the distance from the vertical center of the trigger to the vertical center of the backstrap. The hand that holds the handgun is correspondingly measure from the center of the web between the thumb and forefinger to the point on the index finger that contacts the center of the trigger of the handgun.
Matching these measurements from handgun to hand is critical to proper operation of the firearm. This can be difficult, or easy, depending upon the design of a particular handgun. Nationally known expert, Massad Ayoob, in discussing this issue, uses the example of the Model 1911 .45 semiautomatic pistol.
“The short, relatively easy stroke of this single-action auto-pistol's trigger allows good shooting to be done if the very tip of the finger, or the pad of the distal phalange (or the "farthest-out joint") is in contact. That gives you plus or minus an inch of latitude in fitting the gun to the hand, and it's one of the reasons why I often state that such pistols fit a wide variety of hands.”
But, in contrast, the revolver is a different story. The revolver takes more work to fit to the customer's hand than does the auto-loader. To properly operate the revolver, you must pull the double-action trigger straight back. This requires that the joint of the finger closest to the finger nail be in contact with the center of the trigger. Therefore, with the revolver, you do not have the same degree of latitude in fitting the gun to the hand that you do with the semi-auto pistol.
Additionally, you have to factor in what expert trainers refer to as the requirements of "administrative handling" which includes loading, unloading, checking, dry fire and access to safety/decocker/magazine release, and slide lock/cylinder release. A properly fit handgun will allow the user to manipulate these various functions without excessive readjustment of the basic grip.
A quick test for proper fit requires that you grip the handgun with a good grip. Make sure that you check the weapon first, to be absolutely sure that it is unloaded. Now, grip the weapon. With the revolver, this means that the web of the hand is placed high on the backstrap just under the hump below the hammer. If you are using the semi-auto, the web of the hand is placed high into the tang of the backstrap with the fingers wrapped firmly around the frontstrap. Now take a look at the barrel. It should be in line with the long axis of the forearm, because with a proper grip, the bones of the forearm is the base of recoil support. This allows you to see whether the weapon’s grip is the right size, too big, or too small.
Now, place your finger on the trigger. If your index finger extends past the trigger, beyond the first joint, the length of pull may be too short for good shooting and the finger may be pinched against the frame or trigger guard when the trigger is depressed.
On the other hand, if you have to turn the pistol’s barrel so that it is not aligned with the long axis of your arm, just so that you can reach the trigger, then you must examine what the alignment is telling you about the fit of the handgun. If possible, check for barrel/axis alignment from above the subject’s arm.
If the muzzle of the pistol points to the right (for a right-handed shooter) with the index finger’s first pad on the trigger, the grip is too large. In general, the more shots a semi-auto contains, the more pronounced this problem might be. Revolvers are usually more forgiving, within reason, and grips of different sizes are usually available to correct misalignment.
The proper grip provides the shooter with:
1. A natural point of aim so the sights are aligned without having to do any work to align them.
2. Effective management of both vertical recoil and horizontal recoil upon discharge.
Ensuring proper grip with a firearm that fits the shooter allows the shooter to consistently put rounds where they desire a vital skill where follow-up shots are necessary to stop an immediate threat.