Pump Action

The pump shotgun endures because it is mechanically simple, indifferent to ammunition, and cheap relative to everything else that does the same job. A pump cycles a light target load and a heavy slug equally well because your arm provides the energy, not the cartridge.

That is its real advantage over a semi-automatic for defensive use, where reduced-recoil buckshot may not reliably cycle a gas gun. The cost is that you must run the action deliberately under stress — short-stroking is the classic failure and it takes practice to eliminate. An 18 to 20 inch barrel handles well indoors; longer barrels suit birds and clays.