A friend of mine told me recently he went hunting just once and hated it; every time the borrowed gun went off his thumb hit him in the nose. I didn't have to see the gunstock to know it must have been much too short for John, who stands 6-feet-7.

Most of us are close enough to average size to shoot factory stocked guns comfortably. There is, however, more to shotgunning than coming home without a nosebleed. A gun that fits really well, that lines up immediately with your eye and points where you look, will improve your shooting. What follows is a list of the most important stock measurements, how to measure them, and how to change them.

Length of pull is the distance from the center of the buttplate or pad to the trigger. The traditional gunshop test for length of pull is to hold your arm parallel to the floor, bend the elbow to form a 90-degree angle, and see if the first joint of the index finger reaches the trigger while the butt rests in the crook of your arm. Another is to check your nose when the gun is mounted; it should be about an inch from the base of your thumb (closer and you might punch yourself like my tall friend did). If the stock is of the correct length your cheek will meet it just forward of the midpoint between heel and comb.

Those tests will give you a rough idea of your desired length of pull, but some other factors complicate the question of stock length. Trap and skeet guns, for example, can have extra-long stocks because they are shouldered before the bird appears. Most shooters agree that longer stocks seem to reduce felt recoil. On the other hand, a gun meant for quick shooting at grouse or woodcock in thick cover might benefit from a much shorter stock that won't catch on your clothing as you mount it.

Remember when contemplating stock length that you will often be wearing more clothes in the field than you do in the gun store. I start bird hunting in 70-degree weather in October and close the season at 5 below zero in January, so my upland gun has a shorter stock than I might ordinarily use. Early in the season I add a slip-on rubber recoil pad to lengthen the pull, then I take it off in December to compensate for the extra layers of clothing I put on as temperatures drop.

Using a slip-on pad is an easy way to change the length of pull to see what feels best to you. You'll find, too, when you experiment with different lengths of pull, that you can also shift the gun's balance point perceptibly by lengthening and shortening the stock.

Pitch is determined by the angle of the pad or buttplate and is often expressed in degrees. Calculate pitch by standing the gun upright on the floor with the receiver touching the wall. Measure the distance from wall to barrel at a point 26 inches above where the receiver touches the wall. Each 1/2 inch will equal one degree of pitch.

It's not hard to experiment with different amounts of pitch if you have a gun with a pad or buttplate that's easily removed. Loosen the screws and stick a spacer of some kind at the toe or the heel, then tighten the screws down again. Point the gun at objects on a far wall and you'll see how changing pitch raises or lowers the point of impact.

Some shooters like to alter the pitch of their guns for comfort's sake. I used to have a seven pound, 20-gauge pump gun, theoretically a light kicker, that dug the sharp toe of its plastic buttplate painfully into my chest each time I set it off. I solved the problem by selling the gun, but I what I should have done was cut the stock at an angle to increase downpitch and spread the recoil more evenly across my shoulder pocket. Incidentally, if you cut wood off a gunstock to shorten it, be very careful not to alter the pitch; merely cutting along the vertical will likely leave the gun with less pitch than it had to begin with.

Drop is the vertical distance from the comb to the level of the rib, measured at the front of the comb and again at the heel. More drop should make the gun shoot lower, less should raise the point of impact. Most American field guns have around an inch and half of drop at the comb and two and a half inches at the heel. You can measure drop by laying the gun upside down on a flat surface like a table top (make sure the bead is hanging over the edge) and measuring vertically from the stock to the table at the heel and comb.

Stocks can be straightened by adding moleskin, wood, or various commercially available pads to the comb. More drop can be added by working on the comb with a wood rasp, but be careful: you only have to take a little bit of wood off to change the point of impact significantly.

How do you know if a stock has the right amount of drop for you? When you shoulder the gun, with the stock sitting comfortably just below your cheekbone, you should see a very little bit of rib and the bead when you look down the barrel. The correct sight picture for a gun with front and middle beads is a figure 8, with the beads stacked. If you have to crane your neck just to see over the receiver, you need a straighter stock.

The more rib you see with the gun mounted, the higher it will shoot. Trapshooters sometimes test a gun's fit by resting quarters at the rear of the rib and seeing how many stack up before the bead disappears. For trap, which requires a high point of impact to deal with rising targets, a height of two or three quarters is about right. Most hunters prefer a flatter sighting plane. If you hunt flushing game primarily, though, don't be in too much of a hurry to lower the impact of a high-shooting gun. A high point of impact gives you the advantage of being able to see a towering pheasant or a springing teal and still hit it instead of having to blot the bird out with the barrels.

Cast off or "advantage" is a slight bend to the right that helps the eye line up directly over the axis of the barrels. Few American-made field guns have cast off, although it's fairly common on European doubles. If you find you have a tendency to shoot to the left (for a right-handed shooter) of where you're looking, a little cast off might solve your problems. If you're left-handed, what you want is called "cast on."

Some cast off at the toe, that is, a pad that angles slightly to the right from top to bottom when looked at from the rear, will help shooters who have trouble twisting or canting a gun to make it fit their shoulder pocket. Again, you can unscrew a buttplate or pad at the bottom and twist it slightly to see if some cast at the toe feels right. Then it's just a matter of drilling a new hole, or you could add an adjustable pad of the kind made for trap guns.

Ideally, you should shoot a gun at a patterning board to check its fit. Draw a mark on the board, or on a piece of paper or a sheet, and take several snap shots at it, mounting the gun before each shot. Don't try to correct your aim if the patterns aren't centered on the mark. You want to see if the gun shoots where you look the first time.

The distance at which you perform this test is not all that important. The farther away you are from the target, the more your errors in pointing will be magnified.

Another way to check gun fit is with a Weaver Accu-Point, a glass bead sight designed so you see its red dot only if you're looking down the rib with your head in the correct position relative to the stock. Although Accu-Points are no longer being made, they turn up frequently at gun shows for a few dollars. The Accu-Point requires two holes to be drilled and tapped in the rib, but then it can be removed and replaced whenever you want to check a gun's fit or your own shooting style.

Finally, realize that changing stock dimensions will only help your shooting if your technique is consistent. If you never mount the gun the same way twice, altering the stock may only compound your problems. Before you start hacking wood off a favorite gunstock, take a long hard look at the way you shoot. Better yet, find a shooting coach who can tell you right away whether it's you or your gun that needs work.