Varmint rifle is an English term for a small-caliber precision firearm or high-powered airgun primarily used for both varmint hunting (the elimination of outdoor animals which harass properties) and pest control (the eradication of indoor infestation by destructive species). These tasks include killing three types of pests or nuisance animals that spread diseases or destroy crops or livestock: Small/medium-sized non-game animals such as crows, ground squirrels, jackrabbits, nutria, marmots, groundhogs, porcupines, opossums, skunks and weasels; Non-native feral/invasive species such as starlings, cats, dogs, goats, wild boar/pigs and donkeys; Animals considered to be nuisance vermin destructive to man-made properties and vegetation, crops and domestic livestocks, such as rats, house sparrows, gophers, and small predators such as coyotes and jackals.
Varmint guns fill a design gap between the more powerful big game rifles and the less powerful rimfire firearms. Big game rifles are more suitable for stalking and taking down individual large-sized animals such as reindeer, elk and buffalo at medium ranges, but not adequate for frequent repeated firing. Rimfire firearms (such as the highly popular .22 LR caliber) are best used to shoot small vermin such as squirrels and rats at close distances, and are somewhat underpowered for many outdoor rodents (which are often alert enough to spot hunters from a long distance away and flee or hide underground), small predators such as coyotes and larger feral animals such as goats and pigs. The varmint rifles are very suitable for repeated medium/long-range shots from a fixed firing position, thus fulfilling and overlapping the functional demands with both in terms of hunting applications.
Common design elements
While any rifle of sufficient power can be used to dispatch targets of opportunity (the venerable .30-30 Winchester lever action and the Ruger Mini-14 are common truck guns or ranch guns kept handy for this) the deliberate taking of varmints requires special characteristics more common to target rifles than "normal" hunting rifles.
General characteristics
Varmint rifles can typically be distinguished from other light-caliber hunting or plinking rifles in the use of heavier barrels and (often) omission of open sights. Use of magnifying optics allows for more accurate fire (often on very small, distant targets). Barrels will generally be free-floated, and other accurizing techniques will be performed, either by the manufacturer or the owner. The stocks will generally have wider forends, designed for use on stable sandbag rests, and high combs for easy use with optics.
Since part of the definition of a "varmint" is that it is a nuisance, varmints are not stalked, but rather they are hunted from a fixed position. This makes weight of little consideration in a varmint rifle, so heavy barrels are common. Varmints are also not subject to the same bag limits as game animals are, so far more shots may be fired. The heavier barrel is, in general, more accurate than a light barrel, plus the extra mass helps reduce the felt recoil and absorb the heat from more shots before expanding and potentially reducing accuracy. Folding shooting benches and sandbag rests help provide a stable base for the shooter, allowing the maximum accuracy to be extracted from the rifle.
Calibers
Since varmints are generally smaller animals, large, heavy bullets are not needed. A light, fast bullet gives a flat trajectory, making range estimation less vital for accurate shot placement. Velocities for modern varmint rounds are usually in excess of such as the .223 Remington and some like the .220 Swift can exceed . This allows long range shots with a short time of flight, and little change in trajectory at different ranges (see external ballistics). A bullet drop of only a couple of inches (about 5 cm) is enough to cause a miss on smaller varmint animals; so flat trajectories increase hit probability at long ranges. Fast, lightly constructed bullets have additional advantages of rapidly disintegrating upon initial contact. Disintegration minimizes the range of ricochet particles; and energy release of disintegration kills small animals more quickly than a penetrating wound.