Annealing: Heating metal to soften it. Brass cartridge cases become hard in the neck after repeated resizing.
Splits and separations result. You can anneal a case to restore its ductility by heating it a cherry red, then quenching it in cold water. With steel, such an operation would increase hardness. Brass is different.
Antimony: A metallic element alloyed with lead to increase bullet hardness. In big game bullets, the usual ratio is 97.5 percent lead, 2.5 antimony. A little antimony makes a big difference. Six percent is about the limit. Sierra uses three alloys for rifle bullets, with antimony proportions of 1.5, 3 and 6 percent.
Anvil: A rearward-facing part of the primer or primer pocket against which a striker crushes the soft primer cup, pinching the priming compound. The percussive force and friction ignite the primer, which shoots a jet of flame through the flash-hole(s) behind the anvil.
Ball: Literally, a lead ball used in muzzle-loaders, but also a bullet as in “Ball Cartridge” and a (typically double-base) powder whose hard spherical grains roll and slide like tiny shot pellets.
Ballistics: The science of projectiles in motion, comprising internal, external and terminal ballistics—that is, what happens during the launch of a bullet (internal), the flight characteristics of that bullet (external) and the penetration and upset of a bullet in animals (terminal).
Ballistic coefficient: The ratio of a bullet’s sectional density to its coefficient of form, a measure of the bullet’s ability to cleave the air. Ballistic coefficient (“C” in formulas) is reflected in a bullet’s rate of velocity loss, and in its vertical drop over distance.
Battery cup: A type of primer that comprises anvil and main primer cup inside another cup. Shotshell primers are battery cup primers; modern rifle and pistol primers are not.
Belted case: A cartridge case with a thick ring immediately forward of the extractor groove. The ring or belt serves as a headspacing device and has nothing to do with reinforcing the case. Most belted cartridges are called magnums or belted magnums. But not all magnums are belted.
Berdan primer: A type of primer with no integral anvil. The anvil is part of the primer pocket. Common in European cartridges, Berdan primers were named for Hyram Berdan, an American. Primer flame reaches the powder through double flash-holes, on either side of the anvil. Berdan-primed cases cannot be decapped by the central pin in standard handloading dies. The alternative: a special hook or hydraulic pressure.
Black powder: A propellant comprising potassium nitrate (saltpeter), charcoal and sulfur in specified proportion. Black powder substitutes like Pyrodex can be used in guns designed for black powder, which generates lower pressures than smokeless powder. However, Pyrodex and other substitutes vary in bulk density. To match a charge of black powder, their measure must be taken by volume, not by weight.
Boat-tail: The tapered rear of a bullet designed for long-range shooting (also, “tapered heel”). Standard bullet bases are flat; hence, “flat-base.” The ballistic advantage of the more aerodynamic boat-tail bullet is seldom realized at ranges short of 300 yards or so.
Bore: The inside of a rifle or shotgun barrel. Bore diameter is the measure taken from land to land in a rifled bore, or the inside diameter of the tube before rifling (“land diameter,” as opposed to “groove diameter,” which is greater). “Bore sighting” is a preliminary alignment of the sight with the bore, before zeroing the firearm by shooting at a target from a bench.
Boxer primer: The common type of primer used in centerfire rifle and pistol cartridges in the US Named after a British colonel, this primer has an integral anvil. A central flash-hole makes decapping easy in a die with a central pin.
Brass: Alloy of copper and zinc used to make cartridge cases (also, a collective term to describe cartridge cases, as in “I have lots of .223 brass”).
Bullet: A single conical projectile fired from a cartridge case, usually but not necessarily through a rifled bore (not to be confused with “cartridge,” which comprises bullet, case, primer and powder).
Caliber: A measure of a bullet, from the Latin term “qua libra” or “what pound.” Initially it was applied to weight, but then exclusively to diameter. A .308 bullet is a 308-caliber bullet. Caliber can be expressed in hundredths or thousandths of an inch (.22 or .224). It is part of cartridge nomenclature but cannot by itself describe a cartridge. There are, for example, many cartridges using .308 bullets— and many of them are designated “.300.” The .300 represents bore diameter, the .308 groove diameter or bullet diameter. Case dimensions of the various .300 cartridges are not the same, though all can use the same bullets. You can’t load .300 Weatherby Magnum cartridges in a .300 Winchester Magnum rifle, and shouldn’t fire a .308 in a .30 Gibbs. But the same .308 bullets can be used in any of those cartridges.
Cannelure: Circumferential groove around a bullet to identify it and to mark the proper case mouth location for crimping after seating the bullet in the cartridge case.
Canister powder: Gunpowder ready for retail sales to the public, typically in plastic or cardboard containers or canisters. “Bulk powder” refers to the powders blended to form canister powders in the laboratories and loading rooms of powder manufacturers.
Cartridge: A unit of ammunition, comprising bullet, powder, primer and case. “Cartridge” also applies to shotgun ammunition, but “shell” and “shotshell” are by far the more popular terms.
Case: The hull or shell of a cartridge, the housing that contains the powder and holds the primer and bullet to form a cartridge. “Case head” is the rear portion that fits against the bolt face of a gun and is gripped by the firearm’s extractor.
Centerfire: A cartridge whose primer is a removable unit held in a primer pocket at the rear of the case, in the center of the head. Some early cartridge designations included “CF.” The “.30 WCF” (Winchester Center Fire) is another name for the .30-30.
Chamber: In a rifle, pistol or shotgun, the rear portion of the bore reamed to precise dimensions to accept a cartridge ready for firing. A chamber is big enough to allow easy insertion of the appropriate cartridge, but small enough to prevent undue case stretch when the cartridge is fired. A “chamber cast” is sometimes taken of relic guns to determine chamber dimensions.
Charge: Amount of powder, usually by weight, specified in a load. Charge also includes the type of powder, as in 90 grains FFg or 56.5 grains H-4350. A compressed charge is one that fills the case to a point above the normal seating depth of the bullet, so that the bullet presses the powder down during seating. Black powder charges are always compressed by the ball or bullet, which must be tightly seated to avoid an air space and a pressure wave that spikes when it hits the immobile projectile.
Chronograph: An instrument for measuring bullet speed. Most chronographs record bullet passage over two points by registering the bullet’s shadow with two electric eyes. The distance between the points is known, and when the chronograph comes up with the time interval (hence, “chrono”) between crossings, speed can be calculated. For a long time, chronographs were laboratory instruments. Beginning in the 1970s, Dr. Ken Oehler made them available to shooters with portable, inexpensive models—much like Bill Weaver gave riflemen an affordable, functional rifle scope in the 1930s.
Collimator: An optical device used in bore-sighting rifles and pistols. A collimator attaches to the muzzle. Its screen has a grid you use to align your sight with the bore’s axis. It’s important to shoot at a distance to establish a zero after using a collimator. This instrument merely helps ensure that your first bullets land close to point of aim.
Corrosive primer: A primer whose residue is hygroscopic (attracts moisture), causing rust in the bore. The corrosive agent in many early primers was potassium chlorate. Corrosive priming was discontinued shortly after World War II, when lead styphnate became the primary ingredient in military and commercial small arms primers.
Crimp: An inward bending of the case mouth to bite into the cannelure of a bullet. Crimping increases bullet pull and helps secure heavy bullets with short shanks, such as big-bore pistol bullets. Crimping is also used on dangerous-game ammunition to prevent the bullets in a loaded magazine from backing out under recoil and seizing the magazine. Ammunition for tubular magazines and revolvers likewise warrants a crimp, particularly if recoil is severe. Because there’s some bullet deformation, crimped ammo may not give you the best accuracy. A lot of factory ammunition is crimped, however, and can be expected to deliver good hunting accuracy. Bullets without cannelures should not be crimped.
CUP: Copper units of pressure, a measure of breech pressure obtained by measuring a copper pellet of specified starting dimensions after it has been crushed by a piston thrust outward through a hole in the barrel of a test gun. Copper crushers gauge the pressure of high-performance rifle and pistol ammunition. Lead units of pressure are generally used for shotguns and low-pressure pistol loads.
Drift: Lateral movement of a bullet away from the bore-line during flight. Drift is the horizontal equivalent of drop, which results from gravity’s pull on the bullet. Unlike gravity, the air movement that causes drift is not always present. And when it is, its speed and direction cannot be assumed. Good “wind-dopers” know that wind action (and drift) may differ at different points along the bullet’s path.
Energy: The amount of “work” that can be done by a moving bullet a given distance from launch. Muzzle energy is a common standard, calculated by squaring the velocity of the bullet (fps), multiplying that figure by the bullet’s weight (grains) and dividing the product by 450,240.
Erosion: Wearing of the bore caused by the friction and heat of firing. Erosion occurs whether or not you clean the bore and no matter what type of powder, primer or bullet you use. It accelerates as bullet velocity increases. The most severe erosion occurs in the throat, just ahead of the chamber, where temperatures and pressures are highest. Small-bore, high-speed cartridges with slow-burning powders generate the most erosion. Erosion can be kept to a minimum by letting the barrel cool between shots.
Expansion ratio: Interior case volume divided by bore volume. Cartridges with very high expansion ratios are said to be “overbore capacity.” That is, they have big powder chambers relative to the bore size. Slow powders and long barrels are necessary to get the most from these rounds.
Extrusion: The result of material flow under pressure. Bullet jackets and cores are formed by extrusion in dies. So is tubular powder, which is then diced into short kernels. An extruded primer, in which the striker dimple has a raised perimeter, can be caused by too much pressure, excess headspace or an oversize striker hole in the bolt face.
fps: Feet per second, a measure of a bullet’s speed, like miles per hour for an automobile.
Fireform: Shaping a case to new dimensions by firing it in a chamber of those new dimensions. This is a common practice with non-standard or “wildcat” cartridges but is safe only if the proper headspaces has already been established. A cartridge cannot be safely fired to establish a new headspace dimension!
Firing pin: A rod that strikes the primer of a cartridge when you pull the trigger of a gun. Shapes vary, as do lengths. In early revolvers, a nipple on the hammer nose served the function. The springloaded striker in a bolt rifle can be considered a firing pin, though most incorporate a long rear shank of larger diameter.
Flash-hole: The tunnel connecting the primer pocket to the powder chamber of the case through the web.
Boxer-primed cases have one flash-hole; Berdan-primed cases have two. The flash-hole conducts the primer’s flame to the powder charge, just as a touch-hole introduced spark in early muzzleloaders.
Foot-pounds: A unit of energy commonly used for bullets, the force required to raise a one-pound weight a foot against the resistance of gravity.
Forcing cone: The beveled forward edge of a chamber that brings chamber diameter down to bore diameter. Most commonly this term applies to shotguns, which have relatively long forcing cones.
Form factor: A multiplier determined by the shape of a bullet and used, with sectional density, to determine its ballistic coefficient (C).
Freebore: An unrifled section of bore immediately in front of the chamber. Freebore can include a parallel section or be cut so as to slope gradually from chamber mouth to full land height. It is this variability that causes some confusion. Freebore is loosely used as a substitute term for throat, the section of bore between chamber mouth and full land diameter. But a steep, short throat is not freebored. Freebore describes long throats, which allow the bullet to start moving without interference, reducing upward slope of the pressure curve. Some rifles, notably Weatherby’s, are noted for freebore, which allows more aggressive powder charges than do rifles with shorter throats. Higher velocity results. Also, the freebore lets you seat bullets shallowly, boosting case capacity and, again, velocity. Freebore does not generally improve accuracy.
Full metal jacket: A bullet type designed to maintain its shape during penetration, as opposed to a softpoint or hollowpoint designed to expand and create a large wound channel. Full-jacket (FMJ) bullets are used for some types of competitive shooting, because the jacketed nose is a good airfoil and won’t easily deform in handling. The design also applies to “solids” for hunting large African game. The jacket up front protects the lead core from deformation during entry, ensuring minimal resistance to penetration. In their simplest form, full-jacket bullets are inexpensive to produce. Not only are they standard issue in military cartridges; they’re a first choice for “plinkers” who use lots of ammo for informal target shooting.
Gilding metal: An alloy of copper and zinc commonly used for bullet jackets. Zinc makes up 5 to 10 percent of this alloy, copper the rest.
Grain: In shooting, a unit of weight, not a description of a particle. That is, 54 grains of powder means that charge weighs 54 grains. It may have hundreds of kernels of powder. There are 7,000 grains to a pound, 437.5 to an ounce. Bullets and powder are thus weighed by the same measure.
Grooves: Spiral channels cut or ironed into the bore of a barrel by single cutter, broach button or high-pressure hammers. Grooves and lands (the uncut sections between grooves) comprise rifling, which spins the bullet around its axis, making it stable in flight and more accurate than a bullet from a smooth bore. A bullet’s unfired diameter is, ideally, groove diameter. The lands cut into the bullet, grabbing and spinning it as it is shoved forward on firing.
Hangfire: A delayed ignition of the main charge of powder after the striker hits the primer. Hangfires can be caused by a large air spaces in the case, a weak primer, powder that is hard to ignite. They are ruinous to accuracy because the bullet leaves late, when your sights are no longer perfectly aligned. A hangfire that delays more than a fraction of a second is rare, but misfires should be treated as hangfires for safety’s sake, the rifle kept pointed downrange for 30 seconds before you open the bolt.
Headspace: The measure between the bolt face and that part of the chamber that acts as a cartridge stop when the round is fully chambered. Headspace on rimmed cases is measured to the front of the rim, on belted cases to the front of the belt. Rimless bottleneck cartridges headspace on a datum line on the case shoulder. A few pistol cartridges like the .45 Automatic headspace on the case mouth. Headspace in any firearm is measured with steel “go” and “no go” gauges, precisely machined to minimum and maximum dimensions. A rifle’s bolt should close on a “go” gauge but not on a “no go” gauge. Too much headspace allows the cartridge to move forward when the striker hits the primer. When the expanding gas irons the pliable front of the case tight to the chamber wall, there is nothing to keep the thicker rear of the case (the head) from moving rearward, stretching the brass forward of the case web, sometimes to the point of separation. Released into the chamber through a crack in the case wall, high-pressure gas can damage a rifle and maim the shooter.
Improved: A case design fashioned by “blowing out” a standard cartridge in a chamber of more generous dimensions, typically with less body taper and a sharper shoulder. Result: more powder capacity. Improved cartridges generally take the name of their parent, e.g., the .257 Improved, .280 Improved. Headspace is not changed. If the new chamber does have a different headspace measurement, the factory round cannot safely be fireformed; iIt must first be reshaped to establish proper headspace.
IMR: Improved Military Rifle, a powder designation of E.I. DuPont de Nemours, which replaced the old Military Rifle line of propellants with IMR powders in the 1920s, when four-digit numbers supplanted the two-digit MR designations. In 1986, DuPont sold its powder business to EXPRO, and the IMR Powder Company was established as a testing and marketing arm of that firm. IMR powders are still manufactured for handloaders; only the corporate umbrellas have changed.
Ingalls Tables: Ballistics tables computed by Colonel James Ingalls and first published in 1916. These tables have since served American ammunition makers and ballisticians as the basis for calculating ballistic coefficients and bullet flight characteristics. As with French ballisticians in his day, Ingalls’ work followed that of Isaac Newton, Galileo, Benjamin Robins (who developed the ballistic pendulum), the Krupp factory in Germany (which, with other agencies, conducted firing tests to determine ballistic coefficients) and a nineteenth-century Russian named Mayevski (who fashioned a mathematical model of standard drag deceleration of the Krupp bullet). In France, the Gavre Commission had found a flaw in the assumption that drag on a bullet was proportional to some power of the velocity within a range of velocities. At high speed (above 6,000 fps) there was a sharp rise in retardation. The Gavre Commission developed tables to show this—really, the first ballistics tables ever. British ballisticians came up with a better one in 1909, another in 1929. The Ingalls tables were produced using a bullet much like the one-pound, 1 inch-diameter British projectile with its 2-caliber ogive. They are valid to velocities of about 3,600 fps, at which point the British 1909 tables must be used.
Jacket: A metal covering or envelope that protects a bullet’s lead core from the heat of friction produced in its travel down the bore. Unjacketed lead bullets were sufficient in early muzzleloaders and black powder cartridge guns that kept velocities under 1,800 fps. Higher bullet speeds stripped lead from the bullets, ruining accuracy and fouling the bore. Bullet jackets are typically copper or gilding metal (copper alloyed with zinc), but steel jackets have been used. Jacket material and thickness can affect breech pressures. With jacket design, they also have a lot to do with how an expanding bullet opens in a game animal.
Keyhole: The perforation made by a bullet entering a target sideways. Keyholing is the mark of a tumbling bullet that is both inaccurate and ballistically inefficient. Tumbling can be caused by insufficient rifling twist, a defective bullet, or bullet contact with a twig or other obstruction.
Lands: The raised sections of rifling with a bore. Lands lie between the grooves and engrave the bullet as it is force down the bore by powder gas. Land diameter is less than groove or bullet diameter, so the lands are really what spin the bullet, making it stable in flight like a well-thrown football. Some caliber designations reflect land diameter, some groove diameter. The .300 Savage and .308 Winchester both use .308 bullets in bores with land diameters of .300.
Leade: Same as throat, that section of the bore between the chamber mouth and full land diameter.
Loading density: In ammunition, the ratio of the volume of the powder charge, expressed in grains weight, to the volume of the case, also in grains weight.
Lock time: In a firearm, the interval between release of the sear by the trigger, and detonation of the primer.
LUP: Lead units of pressure, a measure of breech pressure obtained by measuring a lead pellet of specified starting dimensions after it has been crushed by a piston thrust outward through a hole in the barrel of a test gun. Lead units of pressure are generally used for shotguns and low-pressure pistol loads. Copper crushers measure the pressure of high-performance rifle and pistol ammunition.
Magnum: A cartridge (or, by extension, a firearm) of unusually high performance. A magnum designation may indicate the existence of a standard cartridge of the same bore dimensions but lesser power (the .270 Weatherby Magnum drives a .270 bullet faster than the .270 Winchester because it has a bigger case and more powder). But some magnums, like the .264 Winchester Magnum, have no standard counterpart. Magnum rifle cartridges are generally belted; not so the .357 and .44 Magnum handgun cartridges. The term “magnum” may not by itself identify a cartridge, because there are several commercial .300 magnums, all of different dimensions and ballistic potential.
Maximum ordinate: The point at which a bullet reaches its greatest vertical distance above line of sight, typically just over half the zero distance for ordinary hunting bullets in rifles zeroed at normal ranges. “Max ord” can move farther downrange, relative to midpoint, as zero range is increased. That is because a bullet’s arc is parabolic. So the term “midrange trajectory” is really a misnomer for maximum ordinate.
Meplat: The diameter of the flat nose tip of a bullet.
Mercuric primer: An old primer used successfully with black powder arms because the bulky black powder residue absorbed the primer’s residue. But with clean-burning smokeless rounds, the mercury fulminate was left to attack the brass cartridge case, weakening it. Non-mercuric primers arrived when potassium chlorate replaced mercury fulminate as primary ingredient. Non-mercuric, non-corrosive primers followed in the 1940s.
Metal fouling: Deposits of bullet jacket left in the rifling.
Minute of angle: A term describing shot dispersion. A circle of 100 yards radius has 360 degrees of roughly 60 inches per degree on its perimeter. Each degree can be divided into 60 minutes of about an inch on the perimeter (totaling 21,600 minutes). A 1-minute group is a series of shots whose greatest dispersion to the centers of the outside holes in the target measures an inch (really, a minute is 1.047 inch) at 100 yards. A 1 inch group is the same size. But a 1 inch group at 200 yards is a half-minute group. A one-minute group at 200 yards measures 2 inches; at 300 it measures 3 inches. Bullet divergence from group centers increases with distance, though rate of divergence remains the same (or may even decrease as the rotating bullet “goes to sleep” at long range). A benchrest rifle is expected to shoot groups as small as a quarter minute; a rifle for prairie dogs should shoot well under a minute. A big game rifle, however, needn’t be so accurate, because a deer’s chest is a big target. Two-minute accuracy will allow you to keep all your shots in the deer’s vitals out to 400 yards, a very long shot. Most modern rifles and loads are capable of better accuracy, however, and it’s not too much to expect 1-½ inch groups from your hunting rifle.
Mushroom: Shape of a bullet after expansion in game. Softpoint bullets designed for big game are made to mushroom, delivering energy as the bullet slows and plowing a wide wound channel. Frangible bullets for small animals like coyotes and prairie dogs, where penetration is not an issue, are made to disintegrate for a lightning-like kill.
Ogive: The curved portion of a bullet between nose and shank. “Secant ogive” and “tangent ogive” refer to the placement of a compass used to scribe the arc that determines the nose profile. The radius of the curve is typically expressed in calibers. A 2-caliber ogive would be a curve with a radius twice bore diameter.
Overbore: A condition or cartridge characterized by a high expansion ratio; that is, the cartridge case is big in relation to bore diameter. Overbore cartridges have produced the highest bullet velocities, but they don’t operate efficiently in short barrels, and they typically require large charges of very slow-burning powder. Because of high throat temperatures and the exit of considerable unburned powder from the case during firing, throat erosion proceeds more rapidly in rifles chambered to overbore cartridges.
Patched ball: A ball or bullet, usually in black-powder muzzle-loading rifles, that has a cloth or paper patch protecting it from powder gas and sealing that gas behind. Patches also reduce fouling.
Point-blank range: Any distance at which you can hit your target without aiming high or low to correct for the trajectory of the bullet. Maximum point-blank range is the farthest distance at which you can hold in the middle and not hit too low. Point blank ranges vary, depending on the load, the target and the acceptable deviation from center. The less deviation you tolerate, the shorter will be your maximum point-blank range. If you don’t mind your bullet hitting a couple of inches high or low with a center hold (that’s not too much deviation for most big game hunters), you’ll extend your point-blank range farther than if you insisted on hitting no more than half an inch high or low. If you’re shooting competitively at targets, point-blank range is the range at which your target is fixed, the range at which you’ve zeroed. On the other hand, point-blank range is often used colloquially to describe very short-range shooting, where sights aren’t used at all.
Port pressure: In a gas-operated autoloading firearm, the gas pressure at the port, typically some distance down the barrel.
Powder: Here gunpowder, which includes black powder, semi-smokeless and smokeless powder, as well as black powder substitutes. Powder is a granular fuel (not really a “powder”) that burns very fast. It does not detonate from impact as does a primer. Gas formed from burning powder expands to push a bullet or shot charge down the barrel. Powder granules are of various shapes and sizes, depending on their intended use. Coarse, slow-burning powder in large-volume cases move fast bullets. Small cases with big mouths call for powders of faster burn rates. Single-base powders are mainly nitrocellulose, while double-base powders have a significant amount of nitroglycerine. Progressive-burning powders are either shaped or treated to release energy in a controlled way, increasing gas production over time rather than “burning down” from a high initial energy release. Powder charges are measured in grains weight (437.5 grains to the ounce). Black powder substitutes do not all have the same bulk density. They’re formulated to be measured in black-powder measures, bulk for bulk. Labels on shotshell boxes show charges in “drams equivalent,” a designation held over from when the propellant was black powder. A dram is a unit of weight; 16 drams equal one ounce. When smokeless supplanted black powder at the turn of the century, it was of a type known as “bulk powder” and could be loaded in place of black powder “bulk for bulk” (not by weight). “Dense” smokeless powders came later. They took up less space, so neither bulk nor weight measures transferred. A “3 ¼ dram equivalent” is a smokeless charge that approximates the performance of a 3 ¼-dram black-powder charge. It has nothing to do with the amount of smokeless powder loaded.
Primer: A small metal cup containing a sensitive detonating compound which, when crushed by the blow of a firearm’s striker, hammer or firing pin against an internal anvil, throws a spark. The anvil may be part of the primer (Boxer) or part of the primer pocket (Berdan). The spark travels through a flash-hole in the case web to ignite the main charge of powder. You can buy standard and magnum primers (magnums give you a spark of longer duration) and primers for “large rifle,” “small rifle,” “large pistol,” and “small pistol” cases. “Battery cup” primers for shotshells are encased in a larger cup that adds support in the thin shotshell head.
Pyrodex: A black powder substitute developed by Dan Pawlak, who died in a powder fire at his factory in Washington state. Hodgdon powder company bought the rights to manufacture and market Pyrodex.
Rifling: In the bore of a rifle or pistol (and now shotguns designed to shoot slugs), lands and grooves that spin a bullet. Rifling gives any projectile (even a patched ball) greater accuracy and, by keeping bullets nose-first, greater range. Rifling twist is the rate at which a bullet is spun, expressed as the distance it travels while making one complete revolution. A 1-in-14 twist means the bullet turns over one time for every 14 inches of forward travel. The proper rate of twist varies with bullet profile, weight and even speed. In 1879 Briton Sir Alfred George Greenhill came up with a formula that works for most bullets most of the time: The required twist, in calibers, is 150 divided by the length of the bullet in calibers. So if you have a 180-grain .30-caliber bullet 1.35 inches long, you first divide 1.35 by .30 to get the length in calibers (4.5). Then you divide 150 by 4.5 and get a fraction over 33. That’s in calibers, so to bring it into inches of linear measure, you multiply it by .30. The final number is very close to 10, a useful rate of spin for most popular 30-caliber hunting cartridges, from the .308 to the .300 Weatherby Magnum.
Rim: In cartridges, the edge of the case head the extractor seizes to pull the case from the chamber. Rimless cases have a rim behind a deep extractor groove, but it’s the same diameter as the body of the case and does not protrude beyond as does a rimmed or semi-rimless case. A rimmed case headspaces on the rim and does not need an extractor groove. A rebated rim is one that is smaller in diameter than the case body (e.g., the .284 Winchester). British rimmed cartridges are typically said to be “flanged.”
Sabot: A lightweight hull or envelope, typically of groove diameter, that carries a smaller, more ballistically efficient projectile out the barrel, then falls away. A central projectile (commonly a shotgun slug or small-diameter bullet), is spun by the sabot but bears none of the rifling marks. It benefits from the sabot’s large-diameter base during launch but is not burdened with excess weight or diameter in flight. The sabot idea was first tested in French artillery.
Seating: The act of inserting a bullet in a case neck. Seating depth is a critical element in getting the most accuracy from a firearm, and can affect pressures as well.
Sectional density: A bullet’s weight in pounds divided by the square of its diameter in inches. Sectional density and the bullet’s profile or form combine to yield ballistic coefficient, a measure of the bullet’s effectiveness in battling drag in flight.
Spitzer: A pointed bullet, derived from a German term that described the first 8mm German military bullets of aerodynamic shape. Spitzers have a more streamlined form and, thus, higher ballistic coefficients than flat-nose or round-nose bullets of the same weight.
Throat: The unrifled section of bore between the case mouth and full land diameter (also known as leade and, not quite correctly, as freebore).
Web: The solid portion of a cartridge case between its base and the powder chamber. The primer pocket is at the rear of the web, and the flash-hole is drilled or punched through the web.
Wildcat: A cartridge that is not loaded commercially. Wildcat cartridges are designed by handloaders who want something different. They’re made by reshaping parent cases in special dies so they headspace safely. Firing in the wildcat chamber—as with “improved” cartridges”—completes case-forming.
Zero: In shooting, the range at which the sightline crosses the bullet’s path the second time, farthest from the gun. The bullet begins to drop as soon as it leaves the muzzle, but the sightline maintains a slight angle to the bore and meets the descending bullet arc a few yards (typically 25 to 35) from the muzzle. The angle of the sightline brings it into the bullet’s arc again as the bullet’s rate of drop accelerates with distance. That final crossing is the zero range. Zeroing at 200 yards gives riflemen a useful “point-blank” range for most big game rounds. Bullets then strike between 2 and 3 inches high at mid-range or maximum ordinate. They drop 3 inches low somewhere around 250 yards. Bullets with steeper trajectories must be zeroed at shorter range. Foster-style shotgun slugs might call for a 75-yard zero, as does the .22 Long Rifle cartridge in rifles. Many handguns are zeroed even closer.