A shotgun isn't aimed the way a rifle is. There are no sights to line up, no slow squeeze on a still target. You look at the bird, mount the gun, and trust that the barrel is pointing where your eye is looking. That trust only works if two things are true: your dominant eye is the one doing the looking, and the gun puts that eye directly over the barrel when it lands on your face. That's gun fit, and most missed targets in a new shooter's first rounds are one of those two things being wrong.
Which eye is in charge
Your brain favors one eye for aiming, the same way you favor one hand for writing. Roughly one person in three is left-eye dominant — and it is not always the eye on the same side as your dominant hand, which is the whole reason this section exists.
The desk test takes ten seconds. Hold both hands out in front of you and make a small triangle by overlapping your thumbs and forefingers. Pick something across the room — a doorknob, a light switch — and frame it inside the triangle with both eyes open. Now close your left eye. If the object stays inside the triangle, you're right-eye dominant. Close your right eye instead, and if it stays inside the triangle, you're left-eye dominant. The eye that keeps the object centered is the one your brain is using to aim. Do the test three times; if it flips, you have weak dominance — fixable, but worth knowing before you spend money on a gun.
Cross-dominance: right-handed, left-eye
If you're right-handed but left-eye dominant (or vice versa), mounting the gun to your strong-side shoulder puts the wrong eye over the rib. The gun points where your right eye is looking, but your brain is using your left eye to track the bird — so the barrel ends up a foot off and you don't know why. Shooters handle this three ways.
The cleanest fix is to switch shoulders: shoot from your non-dominant side so the dominant eye is over the barrel. It feels awkward for a week and then it doesn't. Many cross-dominant shooters who switch early end up shooting better than they would have on their natural side.
The second is to close or squint the dominant eye at the moment of the shot, forcing the other eye to take over. This works, but you lose depth perception and peripheral pickup of the bird, which matters on fast crossers.
The third is a small dot of translucent tape — about the size of a pencil eraser, stuck on the lens of your shooting glasses directly in front of the dominant eye. It blurs that eye's view of the bead just enough that your brain switches to the other eye for aiming, while still letting both eyes see the bird. Many instructors prefer this for cross-dominant adults because it preserves binocular vision without retraining a shoulder.
What "fit" actually means
A shotgun fits you when, after a clean mount, your dominant eye sits directly over the rib without you having to hunt for it. Your cheekbone — not your jaw, not the side of your face — lands on the comb of the stock, and looking down the barrel you see the bead sitting just on top of the rib. No tilt, no stretch, no squint.
If you have to lift your head off the comb to see the rib, the comb is too low. If you have to mash your cheek down into the stock to find the rib, the comb is too high. Most fit problems are comb height. A comb too low puts your eye below the rib, so the gun shoots low; a comb too high puts your eye above it, so the gun shoots high. This is why adjustable combs and stick-on pad shims exist — small height changes move impact several inches at 40 yards.
The other variable worth knowing is length of pull: the distance from the trigger to the back of the buttstock. Too long, and you can't bring the gun up cleanly — the stock catches under your arm. Too short, and your face crowds the rear of the gun, putting your cheek in the path of recoil. The first sign of a length-of-pull problem is usually a thumb-shaped bruise on your cheekbone after a long day.
A check you can do at home
Stand five feet from a blank wall with a small mark — a piece of painter's tape — at eye level. Verify the gun is empty: action open, chamber checked. Close your eyes, mount the gun the way you normally would, then open your eyes without moving anything.
If the bead sits just on top of the rib pointing at the mark, the gun fits you well enough to shoot. If it's left, right, high, or low, the gun isn't landing your eye where it needs to be — and no amount of practice will swing-correct a fit problem. A gunsmith or a good club instructor can usually fix it with shims, an adjustable comb, or a stock alteration in an afternoon.
Once the gun fits, the next thing to drill is the mount itself. The Mounting the gun consistently drill uses the same wall-mark setup and tells you how many reps to do.
Fit is the quiet half of shooting well. Get it right once, write the numbers down, and the gun stops being something you have to fight every time you mount it.