best achieve the hit on their intended targets. Shooting is also used in warfare, self-defense, crime, and law enforcement. Duels were sometimes held using guns. Shooting without a target has applications such as celebratory gunfire, 21-gun salute, or firing starting pistols, incapable of releasing bullets. Restrictions In many countries, there are restrictions on what kind of firearm can be bought and by whom, leading to debate about how effective such measures are and the extent to which they should be applied. For example, attitudes towards guns and shooting in the United States are very different from those in the United Kingdom and Australia. Canting Canting is an alignment issue that occurs in shooting. Because scopes need to be mounted to a rifle in perfect parallel to the barrel and to ensure the cross hairs sit exactly where a bullet will go (POI), a small variation of even ¼ of one degree can cause great problems at longer ranges. A locking bar holds the mount in a perfect 90 degree to the rail system whereas a non-locking bar system can cant to the left or right. This canting (sometimes called jamming of surfaces) is caused by not matching the clamping surface perfectly to the rail. When tightened down, stress exerted on the base can cause the scope to be off from the POI by as much as several feet at 100–200 yards and gets progressively worse as range increases. Lower grade materials used in manufacturing of scope bases, inconsistent design tolerances from one manufacturer to another and other factors can cause twisting stress and cause the mount to move out of parallel with the rifle barrel. The locking bar system allows for even stress to be distributed and prevent canting of the scope mount. Another form of scope canting is caused by the rings themselves. Some mounts either have two or four screws on top of the scope ring that hold the scope in place. With the two-screw style, the ring usually aligns well but does not have the strength of the four screw system. When tightening the screws of the four screw type, the scope can twist in place, causing misalignment. Shooting positions The National Rifle Association of America defines four basic "competition" or "field" shooting positions. In order of steadiness/stability (the closer you get to the ground, the steadier you are), they are prone, sitting, kneeling, and standing (also