Here are a selection of the most common shotgun gauges (bores). From left to right - 12 Bore, 16 Bore, 20 Bore, 28 Bore and the .410
I use 12 bore, 20 bore and .410
The 12 Bore is very versetile. I shot any from 28 gram cartridges, right up to 46 gram cartridges when I am shooting on the foreshore.
The 20 Bore is my wife's gun. When she uses it, she use 21-24 gram cartridges to reduce the recoil. I use it occasionally for a change and put 28-32 gram cartridges through it. Although I struggle with it as it only weighs 6lb 6oz. I find it difficult to maintain a consistent swing with such a light gun.
My preference is a heavier 12 bore weighing around 8lbs.
I've got two .410s which I use for dog training or when I require a quiet shotgun.
I use cartridge weights from 12.5 gram up to 19.5 grams, depending on whether I need to shoot quietly and discretely.