Bullet Types

First things first, the "bullet" is just the part of the ammunition that gets thrown downrange and impacts the target.  Modern ammunition used in pistols and rifles consists of several parts: the shell casing, the bullet, the powder, and the primer (shotgun ammunition is a little different, but let's not go there now).  One unit of ammunition (a casing, bullet, powder, and primer all put together and ready to use) is often referred to as a "cartridge" or a "round".  Unfortunately, in popular vernacular, cartridges are often referred to as "bullets" even though that's technically incorrect.  The subject of this webpage is bullets, and by that, I mean just the part of the cartridge that gets thrown downrange and impacts the target.

The first major distinction between different bullets is the caliber.  The caliber is a descriptive name, primarily used to avoid confusion between different calibers.  The caliber usually consists of a number indicating the approximate diameter of the bullet, sometimes followed by other dimensions of the cartridge (like a length or power indicator), often followed by the name of the organization that created it.  Caliber is typically expressed in fractions of an inch or millimeters.  So, ammunition whose caliber is ".223 Remington" is approximately 0.223 inches wide and was created by Remington, and ammunition whose caliber is "5.56 NATO" is approximately 5.56 millimeters wide and was specified by NATO.  

Is it millimeters or inches?  The units of the width are frequently not specified in caliber names, and the decimal point is often omitted, and the number of digits used varies, but you normally cannot confuse inches and millimeters, because almost all hand-held firearms use bullets that are less than or equal to 0.5 inches wide, and more than 5 millimeters wide (there are bullets less than 5mm wide, such as .17in which is about 4.3mm wide, but those are most often specified in inches).  So, if you see a number less than or equal to 5, 50, or 500, you can be pretty sure the units are inches.  If you see a number larger than 5, 50, or 500, you can be pretty sure the units are millimeters.

IMPORTANT NOTE:  The number in the caliber name is NOT necessarily the true width of the bullet.  Why?  First, because the caliber often describes the diameter of the barrel bore, but most bullets are slightly larger than the barrel you shoot them out of, so that the bullet will properly engage the rifling grooves and make a good seal against the bore walls when fired.  For example, most .45 Auto bullets are actually .451 or .452 inches in diameter.  Second, because caliber names are used to avoid confusion between different calibers to help people avoid using the wrong ammunition in their gun.  For example, 9mm Luger, 9mm Steyr, 357 Sig, 380 Auto, and 38 Super all use bullets that are .355 to .356 inches in diameter, but that doesn't mean those calibers are interchangeable (they are not), or even that a given bullet of that diameter can be used in any of them (they cannot).  When reloading, sometimes the same bullets can be used in multiple calibers, and sometimes similar calibers use different bullets.  For example, most bullets that are used for 40 S&W ammunition can also be used in 10mm ammunition, but you typically do not want to use a bullet designed for a 380 Auto as your 9mm bullet, even though they are the same diameter (because diameter is not the only factor; things like pressure and case dimensions matter, too).  It can be very confusing.  If you're not sure, ask questions of the bullet manufacturer or retailer before you buy.

SIDE NOTE 1: Most cartridges follow the typical naming pattern described above, but certainly not all of them do (especially old ones).  For example ".30-06 Springfield" is approximately .30 inches wide, and was created by Springfield, but the "06" part is because it was adopted by the US Army in 1906.  As another example, "22LR" stands for "22 Long Rifle", which is supposed to help distinguish it from the original "22" cartridge, and the "22 Short" cartridge, and the "22 Long" cartridge, which are all different (yeah, you read that right... "22 Long" and "22 Long Rifle" are different cartridges). You also need to be aware that people often use abbreviated or slang names for common calibers.  For examples: "9" or "9mm" is short for "9mm Luger", and "22" almost always means "22 Long Rifle", and "223" is short for "223 Remington", and "45 ACP" is slang for "45 Auto", etc.

SIDE NOTE 2: In the firearms world, the word "caliber" is sometimes specifically used to describe the inside diameter of the barrel bore, or the outside diameter of the bullet, as opposed to a cartridge name, as described above.  And that makes sense, because, in engineering, the word "caliber" is often used to describe the inside or outside diameter of things that are round.  But, in a super-confusing twist, in the world of big military guns, like naval artillery, the "caliber" of the gun is actually the ratio of the length of the barrel to the diameter of the barrel bore, so 30 caliber means the length is 30 times the bore diameter.  Wait... what? See also: https://en.wikipedia.org/wiki/Caliber

With bullets of a given caliber, the next major distinction is bullet weight.  Bullets are almost always weighed in units of "grains", abbreviated gr.  For example, with 9mm bullets, typical bullet weights are 115gr, 124gr, and 147gr, but you can certainly find other weights, like 95gr, 125gr, 135gr, and 158gr, especially from companies that sell bullets for reloading.  The bigger the number, the heavier the bullet.  How big is a grain?  A grain is tiny, and was originally derived from the weight of a single grain of barley.  There are 7000 grains in a pound.  There are 437.5 grains in an ounce.  In metric units, the grain is defined as being 64.79891 milligrams, which means there are 15.4324 grains in a gram.  Like I said, it's tiny.

SIDE NOTE: Within a given caliber, heavier bullets are typically going to be longer (since they are the same width, and that extra weight has to go somewhere), but this is not always the case, because of the variety of bullet shapes.  For example, hollow-point bullets are typically longer than round-nose bullets because that void in the tip consumes volume, but doesn't add weight.

Materials / Composition

Material / Composition	Description	Notes
cast lead (L)	Lead bullets made by pouring molten lead into a mold	The traditional bullet
hard-cast lead (HC)	Cast bullets made of a lead alloy that is harder than pure lead	The purpose of the harder alloy is to help prevent lead deposits in your barrel (called "leading"), and to withstand higher velocities and chamber pressures.  For example, the alloy of 92% lead, 6% antimony, and 2% tin is a common alloy for hard-cast bullets.  Sometimes abbreviated "HC".
swaged lead	Bullets made by forming a hunk of solid (not molten) lead into a desired shape by force.	Allows for more precise bullet dimensions and more precise weight distribution / balance (fewer voids/bubbles) than cast lead bullets, so it is typically used for high-precision competition bullets. More expensive than casting.
jacketed (J)	A lead bullet with a harder metal (usually copper, sometimes steel or other) layer bonded to the outside.  Usually further described as FMJ, TMJ, CMJ, etc. (see below)	The most popular type of bullet. The copper jacket prevents leading.  It also allows much higher velocities and pressures without excessive deformation of the bullet when fired. Most self-defense ammo uses jacketed bullets for their higher velocities.  In the past, in-flight jacket separation was an issue, and that can still happen today, but is not common with modern bullets.
full metal jacket (FMJ)	A bullet with a jacket that completely covers the nose and sides of the bullet, but not necessarily the base of the bullet.	The word "full" is used to indicate that the jacket fully covers the exposed part of the bullet when loaded, to distinguish it from partially-jacketed soft-point bullets.  It is not meant to indicate that the lead core is fully encased (especially at the base / bottom of the bullet).  This term pre-dates concerns over lead exposure that total / complete metal jackets address.
total metal jacket (TMJ)	A bullet with a jacket that completely covers the nose, sides, and base of the bullet.	Preferred over a full metal jacket when concerned about lead exposure (such as when shooting indoors), because the jacket over the base of the bullet prevents vaporizing the lead at the base, which can then be breathed in by people nearby.  May differ from CMJ in how it is manufactured.
complete metal jacket (CMJ)	A bullet with a jacket that completely covers the nose, sides, and base of the bullet.	Preferred over a full metal jacket when concerned about lead exposure (such as when shooting indoors), because the jacket over the base of the bullet prevents vaporizing the lead at the base, which can then be breathed in by people nearby.  May differ from TMJ in how it is manufactured.
plated bullets	Bullets that have been electro-plated or chemically plated, usually with copper	Usually cheaper than jacketed bullets. The plating helps reduce leading. The main problem with plated bullets is that the plating can chip or break off when fired at high velocities (usually over 1050 or 1100 fps), so you usually only load them to velocities of similar lead bullets, so you lose some of the benefits of a copper jacket.
coated bullets	Lead bullets that have been coated with something usually intended to prevent leading in the barrel	Usually cheaper than jacketed bullets.  Many types of coatings are used, from powder coats to moly coats to polymer coats, and more.
soft nose soft point (SP)	A partially-jacketed bullet with the soft lead nose exposed (the tip is not covered by the jacket)	Leaving the nose unjacketed is intended to aid bullet expansion, and thus increase damage upon impact.

There are many other types of materials used in bullets, like steel tips or steel cores for armor-piercing bullets, or plastic tips for good ballistic coefficients with hollow-point-like performance on impact, or bullets that contain chemicals that glow when fired to make tracer rounds, or bullets that contain chemicals that explode on impact to make high-explosive rounds, etc., but the ones above are the most common types.

Shapes of Bullets

Shape	Description	Notes
round nose (RN)	Bullet with a flat base, straight sides, and a rounded nose.	The most common / typical modern pistol bullet shape. The nose shape is often an ogive (which is a type of curvature). Confusingly sometimes referred to by military folks as "ball" ammunition, even though it is not ball-shaped.
flat nose (FN) flat point (FP)	Bullet with a flat tip. May have straight sides (see truncated cone), or curved sides (like a round-nose with the tip cut off).	A common pistol bullet shape.
truncated cone (TC)	Bullet with straight, angled sides and a flat tip. Like a cone shape with the tip cut off.	A common pistol bullet shape. A sub-category of flat-nose that has straight (i.,e. not curved) sides that angle in towards the tip.
hollow point (HP)	Bullet with a hollowed-out dent/hole in the nose	The purpose of the hollow point is normally to encourage the bullet to expand (change shape to get wider) upon impact, to do more damage. It turns out that this shape is often more accurate at long distances than round-nose, so it is also often used when accuracy is important.
wadcutter (WC)	A bullet with a flat or mostly-flat nose that cuts a very clean circle (i.e. wad) out of a paper target	Popular with target shooters, to ensure that they get the correct (maximum) score, because a round-nose bullet can leave a deceptively small-looking hole in the paper, causing you to think it missed the higher scoring ring, when it really didn't. The main problem with wadcutters is that many semi-auto guns have trouble feeding wadcutter bullets from the magazine into the chamber.
semi-wadcutter (SWC)	A flat-topped cone-shaped nose with a shoulder.	Cuts a clean circle from a paper target like a wadcutter, but the nose is shaped more like a flat-nose or truncated cone, to enable more reliable feeding in semi-autos.
boat tail (BT)	A bullet with sides that taper down to a smaller diameter (but usually not a point) at the base	This is a more aerodynamic shape, and thus more accurate at long distances. Usually only found in rifle bullets (not pistol bullets)
beveled base (BB)	A bullet whose base is beveled (meaning that the corner/edge where the sides meet the base has been trimmed at an angle).	The purpose of the bevel is usually to make it easier to seat the bullet during reloading, but it also acts like a tiny boat tail, and thus may affect the aerodynamics of the bullet in flight.
hollow base (HB)	A bullet that has been hollowed out at the back / bottom of the bullet.
double-ended (DE)	A bullet that has the same shape on both ends, and thus can be loaded in either direction.	The only one I've heard of is a double-ended wad-cutter (DEWC), which is flat on both ends, and thus a simple cylinder.
cannelured	Generally speaking, a cannelure is a groove around a cylinder. So, any bullet that has a groove around the body of the bullet is described as being cannelured.	A bullet may have a cannelure for a variety of different reasons.  Revolvers typically require a roll crimp to prevent the bullets from being pulled forward in their casings during recoil when other bullets in the cylinder are fired, and the cannelure gives a place for the case mouth to "roll" into, to grip the bullet.  For semi-autos, the problem is reversed... bullet setback during feeding... and the cannelure helps the casing to "grip" the bullet better, even without a roll crimp  Since a cannelure is generically a groove around a cylinder, sometimes people describe the extractor groove at the base of the shell casing as a cannelure. Some bullets that are not intended to be used with a roll crimp have cannelures, sometimes to hold lubricant, sometimes to affect how the bullet interacts with the rifling in the barrel bore.
heeled (a.k.a. heel-base)	A bullet with 2 diameters. The top/front of the bullet that sits outside of the shell casing is the same diameter as the outside of the shell casing, and the back/bottom of the bullet is a smaller diameter, so that it fits inside the shell casing.	This type of bullet was common in the late 1800's. The best current example is 22LR. The advantages of this bullet design are that the chamber and bore are the same diameter (making the gun easier to manufacture) and easier conversion of older guns to using metallic cartridges. The disadvantage of this bullet design is the need to lubricate the part of the bullet that sits outside the shell casing (where the lube can rub off or collect dirt). Most modern bullets are not heeled, so that they can put the lubricant on the part of the bullet that sits inside the shell casing, where it cannot rub off or collect dirt before firing. SIDE NOTE: The .38 was originally a heeled bullet with a larger diameter of .38 inches and a smaller diameter of .357 inches. When it was converted to a non-heeled design, it used that smaller diameter for the whole bullet, but retained its original cartridge name. That is why .38 caliber bullets are actually .357 inches in diameter, and interchangeable with .357 Magnum cartridges in many revolvers.

Note that these shapes are not necessarily exclusive of one another.  For example, there are semi-wadcutter hollow point (SWC-HP) bullets, and hollow-base wadcutters (HBWC), and hollow-point boat-tail (HP-BT) bullets, etc.

Vectan Powder's website has a List of Abbreviations for Bullets

Term	Description	Notes
ball	Slang for a full metal jacket cartridge, usually round-nose	Typically used to describe military ammo. For example "45 ball ammo" is military slang for 45 ACP ammo that uses a full metal jacket round-nose bullet, and "M855 ball" is military slang for green tip jacketed 5.56mm NATO rifle ammo..
brass	Slang for a shell casing	For example: Looking at the floor after a shooting session... "Are you going to pick up your brass?"
cartridge	A single unit/piece/round of ammunition, typically consisting of a shell casing, primer, powder, and bullet combined together and ready to use.	Also known as a round.  Sometimes erroneously called a "bullet" or a "shell".
centerfire	A type of cartridge/ammunition that has the primer in the center of the base of the shell casing.	As opposed to rimfire.
dum dum	Old slang for soft-point or hollow-point bullets designed to expand upon impact to increase the damage done.	The name originates from the facility that designed early examples of these bullets, the Dum Dum Arsenal, near the town of Dum Dum in India. The Hague Convention of 1899 prohibited the use of expanding bullets in international warfare, and so was commonly described as outlawing the use of dum dums in warfare.
GD	Gold Dot	A type of hollow point bullet made by Speer.
GS	Golden Saber	A type of hollow point bullet made by Remington.
HAP	Hornady Action Pistol	The name for a style of hollow-point bullet made by Hornady. A modified XTP bullet with no expansion grooves, intended to be a less-expensive alternative to XTP bullets, for use in competition shooting, where the expansion characteristics are not important. As the name suggests, intended for action pistol competitions (IDPA, USPSA, etc.)
high velocity	Indicates a velocity range that is higher than normal for this cartridge.	As opposed to standard velocity or hyper velocity. Often used with with .22LR ammo to indicate ammo in approximately the 1100-1300 fps range.
HS	Hydra Shock	A type of hollow point bullet made by Federal.
hyper velocity	Indicates a velocity range that is much higher than normal for this cartridge.	As opposed to standard velocity or high velocity. Often used with with .22LR ammo to indicate ammo over 1300 fps.
primer	The part of the cartridge that ignites when compressed by the firing pin or striker, and thus initiates the burning of the gunpowder	On centerfire cartridges, the primer the little disc in the center of the bottom of the shell casing, and the firing pin or striker hits it directly. In rimfire cartridges, the primer is inside the shell casing around the rim, and the firing pin or striker crushes the rim at one spot, which ignites the primer inside.
powder	The part of the cartridge that burns to create the high-pressure gas that pushes the bullet down the bore and out of the gun.	Most modern rifles, shotguns and handguns use smokeless powder. Muzzleloaders and guns identified as being "black powder" guns use black powder.
rimfire	A type of cartridge/ammunition that has the primer spread around the rim of the casing (on the inside of the casing, which is why you can't see it).	The primer is activated when the firing pin crushes the rim of the shell casing, which applies pressure to the primer compound, which ignites it.  Cannot be reloaded by typical reloading equipment. Typically used with smaller cartridges, like .22LR and some .17 calibers.  As opposed to centerfire.
round	A single unit/piece/cartridge of ammunition.	Same as a cartridge.
SAAMI	The Sporting Arms and Ammunition Manufacturer's Institute	A group of gun and ammo makers that set standards for ammunition These standards are why 9mm ammo from any ammo manufacturer will function safely in any 9mm gun from any gun manufacturer.
shell casing	The part of the cartridge that holds/contains the primer, powder and bullet together.	Typically made out of brass, but can be made of aluminum, steel, nickel-plated brass, or other materials (even paper in the olden days).
standard velocity	Indicates a velocity range that has traditionally been typical for this cartridge.	As opposed to high velocity or hyper velocity.  Often used with with .22LR ammo to indicate ammo in approximately the 900-1100 fps range.
subsonic	Subsonic ammunition is designed to travel less than the speed of sound (about 1,126ft/s (343m/s) at sea level at 70degF (21degC)).	Being subsonic provides 2 main advantages... lower noise since you don't get the sonic boom (important for suppressed firearms), and it avoids inaccuracy caused by in-flight transition from supersonic to subsonic for barely-super-sonic bullets fired at longer distances (such as some high-velocity 22LR at 50yds or 100yds).
Wally World	Slang for Walmart, a popular store for buying cheap ammo.
WWB	Winchester White Box	A line of ammunition made by Winchester that comes in a mostly-white box.  Generally fairly cheap.
XTP	Xtreme Terminal Performance	The name for a style of hollow-point bullet made by Hornady. Originally intended for self-defense use, it turned out to be very accurate, and thus has become a top choice for competition shooting. Hornady recognized this, and started making the nearly-identical, but slightly cheaper HAP style of bullet specifically for competition shooting.