While any rifle will work for taking out a varmint, some large caliber guns provide unnecessary overkill. If varmints are a persistent threat to your property, it may be best to have a rifle specially designed for the intended target.
Varmints aren’t big game so they don’t need big game guns. Brands such as Thompson, Savage, Marlin and others offer rifles chambered in smaller calibers for power proportionate to the prey. A .17HMR should be sufficient if squirrels, rabbits and other rodents or small creature infestations are your main problem. These smaller cartridges are also quieter than larger rifles and thus are less prone to scaring away other pests before more shots can be fired. If predatory creatures such as foxes, coyotes or wolves are posing a threat, a rifle chambered in .223 or .25 calibers would be more efficient.
Since most targets will prove to be too difficult or dangerous to approach at close range, varmint rifles are designed for accuracy at a distance. In addition to the generally flat trajectories and high velocities of the small caliber rounds, most of these rifles are bolt-action and either come with a scope are or a designed to easily mount one. Varmint rifles also use heavier barrels than the average small game rifle. The heavier barrels tend to be more accurate than slimmer barrels and can absorb more heat allowing more shots to be fired in a short time for more effective pest control.