Comb height is the one dimensions that seems to worry shooters more than any other and yet it is the easiest to get right. Before you can successfully shoot with a shotgun you must first be able to see your target and you cannot do that if your comb is too low. Your comb height needs to be high enough to allow you to see along the rib without lifting your head. How much of the rib you see is entirely your own personal preference so long as you can see it. You need to see some rib as well as the beads because if you don’t you are giving away a major visual aid. The dark line of the rib in the peripheral vision acts like a pointer to the target and is much more visible than the bead alone. I often read that you can alter the point of impact by raising or lowering the comb because the eye acts like the backsight on a rifle and lifting it makes the gun shoot higher. Sorry, but this is total nonsense. When you shoot a rifle with open sights you have a front sight and a backsight but you also have an eye, same as with a shotgun but the shotgun does not have the backsight. We do sometimes have a middle bead on a shotgun, the purpose of which is to check alignment and ensure that we are still looking down the centre of the rib but it is not a backsight, neither is the eye.
Shotgun shooting is the art of hitting a moving target and we do this by looking at the target, not by aiming at it. The beads on a shotgun are only intended as an aid to assist in keeping the head on the stock. We rely on the gun pointing where we are looking to hit the target. All of us have the inborn ability to point accurately and the essence of shotgun shooting is just that – look at the target and the gun will follow the eye. It matters not if your eye is down flat on the rib or way up above it. So long as you look at the target and not the gun you will hit what you are looking at. If you are looking over the rib and parallel to it the height does not matter. The problems arise when you try to aim a shotgun by sighting along the rib and using the bead as a sight. If you do this with a high comb the gun will shoot high but that is not how we shoot a shotgun. A high comb has many advantages over a low one, the most important being improved visibility and quicker acquisition of the target. The head up position is a natural one and vision over the rib is much better than vision along the rib when the head is crammed down on the comb with only the bead visible. Try it yourself and it will be immediately obvious. The secret is looking at the target and not the gun.
High rib shotguns are really only encouraging us to use a head upright natural stance. The same is possible without a high rib if you focus on the target and ignore the fact that you are looking down on the rib. A high rib is only lifting the rib from the barrel up into the line of sight as a kind of mental crutch to visually convince us that the comb height is less than it actually is. Interestingly, I have noticed that those using a high rib actually benefit from seeing a little more rib than normal because the side of the rib, to a two eyed shooter, is very visible to the non aiming eye and can cause a temporary master eye problem. Lifting the comb slightly gives a clearer view of the top of the rib to the aiming eye and prevents the other eye from taking over.
In short, the only comb height that is wrong is one that is too low. If your comb is too low you restrict vision of the target and promote using the beads as sights and trying to aim at the target. With the head up you have a clear view of the target with the rib in the peripheral vision and will shoot quicker and more confidently.