All sporting arms are point target weapons designed to engage a single target. Area weapons like artillery have no part in the civilian world. Many definitions of various firearms are political in nature as they were defined by law. Rifles were at a minimum of 16 inch from breech face to the muzzle. This was done to accommodate all the M1 carbines that were in the hands of many civilians. The shotgun is 18 inches or more, barrel length set to prevent the use of sawed of weapons preferred at the time by the criminal element. Handguns have no shoulder stock and a barrel length of 15 inches or less and are required to have some sort of rifling. This is to prevent handguns chambering shotgun shells.
Shooting is 3 Dimensional
A firearm is a three-dimensional exercise. You have the horizontal element and the most variable is the wind. The vertical includes the arc of bullet travel and range. Not only is range to the target for the actual hit, but you must consider penetration as well. For game the projectile must be capable of penetrating to the vital organs to cause tissue trauma and central nervous system disruption.
30 Caliber Weapons
The American shooter is enamored by thirty caliber weapons, by far the most popular caliber in the US. The 30-06, 308 Winchester and the 30-30 garner more than their fair share of the arms carried by the American hunter. Not that other calibers are not represented, and the thirties are getting kind of big for varmints. The reason for this is that the 30-40 Krag was the first smokeless powder caliber adopted by the military. This in turn was followed by the 30-06 and then the 7.62x51mm NATO. We have a long history of military adoption of the thirty caliber weapons.
Handguns follow a different path. In use the .45 caliber handgun rained supreme for many years. First, we had the 45 Colt, then the 45 ACP. The 38 Special and 357 where the police caliber of choice for many years and remained so until the adoption of semi-automatics and vast majority of those were 9x19mm. But for hunting the .44 Magnum, 454 Casull, 480 Ruger and 500 S&W. It is the single shot guns like the Thompson/Center known for accuracy and popular not only as hunter but metallic silhouette competition. They come in .223 Remington up to 30-06. Rifle rounds in a handgun. SSK Industries also make a Contender and will handle up to 270 Winchester to 30-06. Most of these single shots, also available in handgun calibers are barreled from 10 to 15 inches. For the rifle rounds the longer the barrel the better, to remain a “handgun” must stay 15 inches or less.
Concealed Carry Guns
For concealed carry the most popular is the 9mm Luger, then the 45 Auto and finally the 40 S&W. For the ultimate in factory loaded semi-auto one needs to consider the 10mm. If you can tame it, you can even use it in the field. Don’t know why the .357 Sig isn’t more popular, lot more powerful than the 9mm, but only adopted by the Secret Service while the FBI is more 10mm and 40 S&W oriented.