gas-piston, piston-driven
These terms are short-hand for a gas-operated firearm action, and are usually used when describing AR-pattern rifles that have been converted to gas-operation, rather than using the gas-expansion system originally designed for the AR.
gauge
Gauge is the American measure of shotgun caliber. In Europe, the same measurement is referred to as "bore."
Barrel gauge is a system of measurement that refers to the number of solid lead balls that can be cast from a single pound of lead, so larger gauges correspond to a smaller diameter ball. If you melt a pound of lead into twelve equally sized balls, the diameter of those balls is 12 gauge, and a barrel with the same diameter is also 12 gauge. In short, a 12 gauge barrel is a barrel that has a bore of the same diameter as a .083 lb (1/12 lb) lead ball.
Barrel gauge is a system of measurement that refers to the number of solid lead balls that can be cast from a single pound of lead, so larger gauges correspond to a smaller diameter ball. If you melt a pound of lead into twelve equally sized balls, the diameter of those balls is 12 gauge, and a barrel with the same diameter is also 12 gauge. In short, a 12 gauge barrel is a barrel that has a bore of the same diameter as a .083 lb (1/12 lb) lead ball.
group, grouping
A group is a cluster of shots in a target, used to measure accuracy. Groups should be at least 3 shots, but greater numbers of shots provide more reliable results. Group size is determined by measuring the distance between the centers of the two bullet holes that are farthest apart. Measuring from center to center ensures that variations in bullet caliber (diameter of the hole) will not affect the results in a competition between shooters using different calibers.
A single shot is not a sufficient measure of accuracy because it does not guarantee repeatability. Competitive shooters may not accept the results of groups of less than 10 shots.
A single shot is not a sufficient measure of accuracy because it does not guarantee repeatability. Competitive shooters may not accept the results of groups of less than 10 shots.
grain (gr)
Grain is a particularly confusing term because its abbreviation is easily mistaken for gram (g), and grains are commonly used to measure the mass of both bullets and powder. A typical 5.56 NATO round may fire a 62 grain bullet and be loaded with 24 grains of powder. The same measurement is used for both powder and bullet. Originally, the grain was an unstandardized unit of measurement based on the average weight of a wheat seed, but the unit has since been standardized to exactly 64.79891 milligrams.
gunpowder
Gunpowder is a common name for black powder, though it is often (improperly) used to refer to any firearm propellant.
See also: smokeless powder
See also: smokeless powder
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