The 12-gauge has a nominal bore diameter of .729 inch and a standard 12-gauge load is 1 1/8 ounces of shot. The standard 16-gauge load is 1 ounce, and the standard 20-gauge load is 7/8 ounce. If you can only have one shotgun, and you want to shoot a little bit of everything with it, better make it a 12 gauge. This ballistic advantage comes from the shorter shot column of a 12 when compared to any of the smaller gauges firing the same amount of shot. For example, one ounce of shot makes a shorter stack in a fat 12-gauge shell than it does in a skinny 20 gauge shell. A short shot column means fewer shot deformed by friction on their trip through the forcing cone, down the barrel, and out through the constriction of the choke. 1 ounce of shot in a 12 gauge has a column .690 inch long. The same ounce of shot forms a column .968 inch long in a 20 gauge, and 1.21 inches long in a 28 gauge. This means that 12 gauge guns pattern better than the smaller gauges with the same amount of shot, or just as well with more shot. The ideal home defense shotgun would consist of a short barreled model, 18- to 22- inches, chambered for 12- or 20-gauge. Recommended action would be pump or autoloader. Models worth considering include the Remington 870 pump action series, including the Police model and the nickel plated Marine Magnum; the Mossberg 500 Special Purpose, 18.5-inch barrel pump action; the Beretta 1201 and the
Benelli Super 90 autoloaders; and the Winchester pumps: Defender, Camp Defender, and Stainless Marine.