I am going to categorize weapons. The "lowest form" of firearm in this categorization is basically a "single shot" .22LR gun. I call this category A. A single shot gun chambered in .22LR is an example of a category A weapon, and also a "black powder" musket. The first firearms in history were category A weapons, single shot guns that could be carried.
The next rung up the weapons ladder is category B; these are firearms with more than one round capacity, but are inherently limited to under 11 rounds typically in their internal magazines, and they require manual work to prepare the gun to fire a second round. Category B includes internal-magazine fed guns like rifles and shotguns, as well as revolvers that require manually setting the hammer each shot. Typical examples are "hunting" rifles and shotguns, except for any semiautomatic guns like semiautomatic shotguns that are internal-magazine fed. "Actions" are "bolt action," "lever action," and "pump action," which are different ways that manual work is required to prepare the gun to fire another round. Pump action, bolt action, lever action, and manual revolver guns fall into the category B.
The heaviest type of category A or B weapon is a single shot or bolt action rifle, that fires the same round as the category F (see below) M2 machine gun.
The next rung up is category C, which includes automatic weapons, in the sense of "semiautomatic." They are automatic because in the classical sense, upon firing a round, they automatically prepare themselves to fire a second round, but they do require a second trigger pull to actually fire again. They are automatic, contrasted against category B guns, which require some manual work to prepare a second round to fire. Category C includes all those guns fed from internal magazines, where the capacity is no more than 10 rounds, and those that fire semiautomatically, which is one round fired per trigger pull. Category C also includes semiautomatic guns that are fed by a "detachable" magazine that is limited to a maximum of 10 rounds. This includes handguns like Glocks and 1911s, though the 1911 classically ("single stack") is already limited to a maximum magazine capacity of seven rounds without using a magazine that protrudes from the bottom of the magazine well, to make room for up to ten rounds. Category C also includes AR and AK pattern semiautomatic rifles with the same 10 round limit imposed upon the capacity of their detachable magazine.
Category D denotes the same weapons as category C that are artificially limited in the maximum capacity of their detachable magazines, and if there are any artificially limited internal-magazine fed guns, when the limitation is removed, they also are in category D, so long as they are semiautomatic. There is no limit to the feeding capacity in category D, including up to "belt fed," which is basically limitless capacity. Category D includes all those weapons from category C, but without limitation on their feeding capacity. This would include the newer "double stack" 1911 patterns, but classical 1911s are not in this category unless they are fed from a "drum style" magazine, due to their inherent capacity limitation.
The heaviest type of category C or D weapon is a semiautomatic rifle that fires the same ammunition as an M2 machine gun, which is basically the lightest weight category F weapon.
Category E include all weapons capable of firing "fully automatic," which is that it will fire so long as the trigger is pressed down, and there is ammunition feeding. Some category E weapons are machine guns, and only fire in "fully automatic," and others are selective fire rifles, that are capable of being set to fire in semiautomatic, and in fully automatic (or "burst," which is between semiautomatic and full auto). Category E includes most of the same patterns of guns in categories C and D, with the distinction that they are capable of firing "fully automatic." In sum, category E are all machine guns and selective fire guns that can be carried (including "machine pistols" which fire pistol ammunition in full auto, e.g. Uzis), and category E forms the upmost rung of the category of "small arms."
The heaviest weapons in category E are called "SAWs," which stands for "squad automatic weapons," which are in some cases identical in operation to some selective fire rifles and machine guns, except that they can fire continuously for a much longer time before malfunctioning due to excessive buildup of heat. A famous SAW is the M60.
And so category F are not "small arms." Category F weapons cannot be, and aren't carried. Category F includes the M2 machine gun, along with all other firearms that are too heavy to carry, which I generally call "canon." These weapons must be mounted, either to a vehicle like a tank, to an aircraft, or to a ship, or onto a trailer or a building, or right onto the ground, but they are too heavy to carry, and so they are not small arms. Category F weapons are machine guns like the M2 that cannot be carried, and canon.
The heaviest category F weapons are canon that were in times past mounted to navy battleships. The heaviest automatic category F weapons are those mounted to ships, aircraft, and land vehicles, and to the ground /in concrete.
