Rifles come in many calibers, styles, types of action, lengths, stocks types, and finishes. The rifle you choose will depend upon its intended use and the owner's preferences and physical abilities.
Shotguns come in varying calibers from 410 gauge (smallest) to 10 gauge (generally the largest).
General configurations include double-barrel (two barrels side-by-side), over & under (two barrels one on top of the other) and single barrel (one barrel only). The double-barrel shotgun holds two shells at a time, one for each barrel. The over/under shotgun also holds two shells, one in each chamber.
The single-barrel shotgun has the most configurations. There are single-shots, which hold one round at a time. The pump shotgun has a tube-feed which holds 2 - 7 shells. After each firing, the pump action must be used to empty the chamber of the old shell and feed a new shell into the firing chamber. The semi-automatic shotgun is similar to the pump shotgun in its capacity, but you only have to "cock" it once. After each firing of the semi-automatic shotgun, the old shell is ejected and a new one fed into the firing chamber. Newer tactical shotguns have two barrels with up to seven shells in the two magazines for a total of 14 shells with one in the chamber.