Jake cradled his magnum as he dove across the doorway and rolled to his feet. He shoved a fresh clip into the Glock and clicked off the safety. A dithering shadow in front of him was the zombie, and he pumped slugs into it, the casings dinging on the floor around him as the kickback beat his hand with every shot.
If you don't spot the seven errors in this paragraph, you probably aren't a gun nut.
If you know the difference between .223 and 5.56 mm, and why H&K discontinued experiments on spoon tip ammunition, you probably are.
So how to handle readers who are the latter when you're a writer who's the former?
Here's a down and dirty summary. It is not complete, but hopefully a good starting point to narrow down the research.
The earliest firearms were "hand gonnes" or small cannon mounted on sticks. These were simple tubes with a touchhole for a hot match or ember.
Quickly, these developed into matchlock weapons, where a primer pan filled with a finer powder to hasten ignition was placed at the breech (rear), and a serpentine mechanism with a slow match - a cotton cord soaked in saltpeter - ignited it. This mechanism evolved to spring the coal into the pan for more precise fire. Almost none of these weapons had sights to speak of.
Sights were added early on when some target muskets were rifled - equipped with spiral grooves to grip the patch (and later the lead ball directly) to spin it for improved accuracy. Basic physics says that certain weights, speeds and lengths of bullet work better with certain rifling rates. It is possible to have bullets fly all over the place if they are not properly matched to the weapon.
Further development led to the wheellock - a clockwork sprung wheel to strike sparks against flint. Next came the snaphaunce and flintlock - the lock snapped a flint into a hardened steel frizzen, which also covered the pan containing the priming powder. These weapons consisted of lock, stock and barrel, hence the phrase.
Then someone developed the concept of a paper cartridge with pre-measured powder . Bite off the end, pour in the powder, the paper becomes wadding, and ram the ball down. Occasionally, a stray spark or coal will cause a discharge while loading. There are ways to minimize this, but in battle, sooner or later it will happen. Hopefully, it will just cause a puff and a scorch. It can sometimes mean a ramrod whistling through the air or a ball in the wrong place, meaning anywhere you don't intend for it to go. For combat loading, the ball was dropped down loose to speed the process. Accuracy lacked, but 4-6 ranks of musketeers firing in volley kept up a steady rain of lead.
The next step was the percussion lock, using stamped copper caps containing a sensitive explosive such as mercury fulminate. The rate of fire with percussion rifles was actually slower than with flintlocks, down from about four to about three aimed shots per minute. However, the reliability increased dramatically. Instead of fouling after 4-5 shots, a musket might last a dozen or two. Pointed bullets that functioned better than balls came along as well.
If the weapon was built with a rifle barrel, it was called a rifle musket. If the existing smoothbore barrel was "scratch rifled," it became a rifled musket. A short rifle, typically for cavalry, was called a carbine. A short musket might also be called a musketoon. Early muskets were approximately 60 inches long, with the carbines 4-6 inches shorter. This is a massive plot hole in "The Highwayman." If Bess's hands were bound behind her with a musket under her breast, reaching the trigger is an utter impossibility, unless she has arms like an orangutan.
Single shot breech loading rifles came in the mid 1800s, and had one of two mechanisms, either loaded after opening the breech with a lever, or later by "breaking" the weapon open at the breech. The former was more common for military weapons, since the weapon was stronger for bayonet and club use.
From then on, firearms used fixed cartridges of ammunition, consisting of a cartridge case (not "casing"), a primer, propellant, which changed from black powder (gunpowder) to cordite and other nitrated celluloses to modern smokeless propellant (not "gunpowder"), and a projectile or bullet (not a "slug" except in the case of certain shotgun loads). Rifles and pistols are measured in caliber, which is the diameter of the bullet in inches and will usually have a designator (.460 Weatherby Magnum, .600 Overkill, .30-40 Krag, .38 Colt). If there is a second number after a dash, it generally refers to propellant load (.30-30 Winchester). If there's a decimal after a slash, that's usually the bullet size and the first number is case diameter (.500/.465 Nitro Express). Caliber may also be expressed in millimeters (9mm Luger, 8mm Lebel, 7mm Mauser). Some rounds are referenced by length (7.62X54R Russian. The 54 is cartridge length in mm and the "R" means a rimmed cartridge). Light ammunition may be rimfire - the case contains primer in a soft rim. These are generally very low power and not reloadable. Centerfire is often Boxer primed - with a central hole for the primer flash. These can have the primer punched out and can be reloaded. Some is Berdan primed - several holes around the primer perimeter. These require special tooling to reload and generally are just disposed of.
Rimmed cartridges are generally used for shotguns, revolvers, lever actions. Rimless cartridges with a groove for an extractor to hook into are generally used for autoloading pistols and rifles, and modern hunting rifles. Rimfire ammo is rimmed. Rims can get in the way of the mechanism, but make proper seating in the chamber easier.
Around this same time (1860s-1870s), bolt action and lever action rifles came along, with a tubular magazine under the barrel. Round nosed bullets must be used, because pointed bullets resting on the primer of the cartridge ahead are potentially disastrous. Lever actions have the traditional lever underneath as seen in Western movies. The advantage is not having to remove the weapon from the shoulder and affect sight picture to cycle the action, so they are fast. However, the action is generally not as strong. Bolt actions require raising and pulling a handle on the bolt to the rear and forward again, which is harder to do without affecting sight picture, but the rotating lugs on the bolt lock into recesses in the receiver or barrel and are much stronger.
Repeating rifles contain a magazine to supply ammo and a bolt to seal the breech with the cartridge inside the chamber of the barrel. The firing pin is usually inside the bolt and strikes the primer after being struck by a sprung hammer, released by the trigger. The core part that everything attaches to is the receiver.
Pump or slide actions with the slide under the barrel can combine some positive attributes of both, but the sliding action affects certain stances.
The next development was a magazine that fed ammunition vertically from a stack. These were initially loaded by "en bloc" clips inserted down into the magazine. A clip holds ammunition. A magazine feeds ammunition. A clip goes into a magazine. Typically, an empty clip falls loose or is ejected as the last round is fired. With rare exceptions, such as the US Garand and Italian Carcano, en bloc clips fell out of favor before WWI. A charger, or stripper clip, fits into a recess so loose ammunition can be pushed down into the magazine, either while it is mounted on the weapon or detached. The charger is then manually discarded.
Detachable magazines consist of a body, follower that follows the last round, a spring and a base plate. They are not clips (though commonly referred to as such), as they contain springs to feed the ammunition. They usually latch into the bottom, more rarely the side or top of the weapon, and are removed with a lever when empty. Detachable magazines aid in quick unloading for safety and maintenance. Early magazine rifles continued to be loaded by chargers. Eventually, generals concluded that multiple magazines made loading faster. Modern troops typically carry magazines of 30-45 rounds capacity, and carry 6-10 of them. We've gone from a potential dozen rounds for a muzzle loader, to 50-70 rounds for early breech loaders, to 210-300 rounds or more for current troops.
Less common magazine types include rotary, coiled drum and flat drum. These can be treated similarly to box magazines for purposes of loading and using.
Self-loading rifles, also called semi-auto, use the power from firing to load the next round by cycling the bolt back against a spring. This can be done by recoil action, gas pressure in the barrel against the cartridge (blowback), or by bleeding gas off into a tube or piston thrown back against the bolt. The latter is more common with more powerful cartridges. The mechanism in a self-loader absorbs some of the recoil, which is the correct term for the force opposite the discharge.
Automatic rifles continue to fire until the trigger is released or ammunition depleted. Select fire rifles can fire semi or automatic by switching a lever.
Battle rifles are generally powerful enough to take large game (cow or elk sized), or people at 500-1000 meters, and may or may not be select fire. Assault rifles are less powerful, intended for people at under 500 meters, and are generally select fire and fed by detachable magazines. The irony here is that iron sights are almost never good beyond 500 meters anyway, and 90% of military engagements are under 100 meters.
Modern carbines are short, light rifles (20-30 inches overall) that may fire assault rifle or pistol cartridges. If select fire, they may be categorized as submachine guns. There is some leeway in these terms depending on who's defining them.
There are folding, collapsible and detachable stocks for many weapons, and interchangeable grips, slings, mounts and accessories. Earlier weapons and modern hunting guns are often sculpted or customized for a given owner. The former is more versatile and cheaper than the latter.
Nomenclature varies. In the US Army, a gun is a support weapon such as a machine gun or artillery. In the US Air Force, anything that shoots a projectile from a barrel is a gun, whether it's a GUU-5P carbine or a 105mm howitzer in an AC130 gunship. In the US Navy, guns are typically deck or shore mounted cannon. Check what's appropriate for the group you are writing about.
Machine guns are automatic-firing support weapons. Early ones loaded from a feed tray, or a cloth or metal belt with loops for cartridges, or from box or drum magazines. More rarely, they fire from a flat drum atop the receiver, or a belt which may be in a box or drum. Most modern platforms use a disintegrating link belt. The links separate from the cartridge as it is fed into the chamber, and could be gathered and reused, if necessary. Some will of course get stepped on or mechanically bent if there is a malfunction. Machine guns typically fire from the open bolt, meaning the cartridge does not get fed until the trigger is pulled. This reduces "cook offs" of ammunition firing from residual heat in the barrel. Machine guns typically are heavier than rifles - 20-35 pounds - early ones may have a water-filled jacket for cooling, and often require a crew of two to three. They may be mounted on vehicles or tripods, and usually come with extra ammunition belts, spare barrels to change when they get hot, and tools. At firing rates of 400-1400 rounds per minute, and ammunition costing 20-70c per round, machine guns are very expensive to operate as well.
Shotguns started as muzzle loaders, and can be break action with one, two, or very rarely, three or four barrels. They can be pump action (very common), revolving, lever or bolt action (unusual), or self-loading (common). Lever and pump guns are usually tube magazine fed. Bolt action usually have a detachable box magazine. Self loaders are usually tube or box fed. Shotguns are generally smoothbored, not rifled. They fire a cartridge consisting of hull or shell (the only time "Shell" is appropriate short of artillery), primer, propellant and a mass of shot, or a single large slug. Shot varies by size and density depending on the target. Dedicated slug guns are sometimes rifled to shoot more accurately, but are still shotguns, not rifles, as long as they use shotgun ammunition. Shotguns are typically hunting weapons, but are also used for police or military use for breaching doors, or for close quarters combat. They are usually measured in "Gauge," which was the number of round lead balls per pound. Gauges use to range from 4 down to 32, but 12 and 20 are standard now, with 16 and 10 being unusual. 28 gauge is reserved for certain bird hunting. .410 bore (not gauge), is used for very light game or for small shooters.
Early pistols operated as early rifles did. In the 1830s, the revolving pistol, with multiple percussion chambers in a cylinder was invented. This evolved into the single action cartridge revolver, requiring cocking an external hammer for each shot, then the double action revolver that also allowed direct trigger pulls to fire. Some modern ones are double action only with no external hammer. A self-loading handgun is categorized as a pistol. Pistol and revolver are no longer interchangeable terms technically, with a very few exceptions. There are single-shot break action and cannon breech pistols for hunting and target shooting, and bolt action single shot and repeating pistols as well. These are generally not small. Autoloading pistols are usually recoil or blowback operated. Revolvers generally don't have external safeties, nor do GLOCK pistols and some concealable pistols.
Watch your thesaurus. Revolver, pistol, automatic, magnum and other terms may all refer to a handgun, but likely not the same handgun. The basis of a handgun is called a frame, and self-loaders normally have a slide around the barrel instead of a bolt inside.
Typical handgun fights take place under 10 meters, often under 3. The very short sight radius and lack of supporting mass greatly affect the range. Nor are handguns as effective as rifles. Dirty Harry's .44 Magnum is about as powerful as a standard assault rifle. At 400 meters, an assault rifle is as powerful as a .45 Auto is at the muzzle. Remember that assault rifles are light and low power as far as rifles go.
Sights have advanced from a simple bead at the muzzle. Open sights with adjustable ramps and notches at the rear and a friction fit front sight are popular for many hunting rifles. You adjust them with a light mallet. Modern military and hunting rifles usually have a rear aperture "peep" sight and a post front sight. These are adjusted with screw threads. Increasingly, optical sights are popular, and many commercial rifles are sold without any sights so the user can add their own. The common telescopic sight has a cross reticle, and may also have marks for estimating size and range. Reflection off the objective lens can be reduced with a metal mesh or pantyhose. Head up display sights display a reticle on a screen that makes targeting very fast. This allows one to keep both eyes for better awareness. There are adapters for these for magnification or night vision. Laser sights place a red, green or infrared dot on the target, but there is a risk of being observed in return. All sights have to be zeroed for a pre-chosen distance, and rise and fall accounted for at other distances. Most modern military and many civilian weapons have standardized 1" rails, also called 1913 or Picatinny rails after the US Army arsenal that invented them. These rails have numbered slots to make mounting optics or accessories consistent.
Flash suppressors reduce flash, and more importantly, direct it away from the shooter's sight plane. Muzzle brakes help reduce recoil and muzzle climb by directing gases to the sides or rear. Suppressors, commonly called silencers, reduce muzzle flash, and can reduce muzzle noise by 35 dB or so, but rarely actually silence a 110-150 dB report. Subsonic ammo helps by eliminating the supersonic crack of travel. Tuning the propellant to ensure it is consumed in the barrel reduces flash.
Firearms malfunction. Revolvers are less prone to do so, but if they fail, they generally cannot be fixed without tools, especially if a bullet jams between cylinder and barrel, and may be beyond repair depending on the problem. They are fitted to tight tolerance and hard to work on, except for minor things such as replacing springs, sights and grips. Autoloaders may fail to feed (cycling the action will usually fix this), fail to eject (remove the magazine, cycle. If that fails, push the empty out with a cleaning rod), stovepipe - empty case stuck in the action (Cycle the action). They are usually easier to fix than revolvers. Modern spare parts are readily interchangeable with minor fitting. In any firearm, the magazine and feeding mechanism are the usual failure points. It is rare but not unheard of for barrels to fail catastrophically (explode), bolts to rip out of receivers, cartridges to burst.
Guns do not "go off." No matter how broken it is, outside agents must cause it to fire. Certain guns can fire if jarred or jolted. Most modern guns have multiple safety mechanisms to prevent this. If someone has a gun "go off," it means they screwed up.
Maintenance involves cleaning first and foremost. Black powder and early propellant, as well as some primers, leave corrosive residue. Mechanisms require cleaning and oiling. Eventually, springs and sear surfaces wear out. Precision firearms will need retuned to keep them to spec. Earlier firearms will suffer wood warpage from heat and humidity. Wood can rot, plastic can be affected by solvents, wear and tear will damage finishes. Surfaces can be blued by heat or chemical action, oxidized or phosphated, or painted with various lacquers, varnishes, epoxies. Anodizing, powder coating and hydrographic transfers are common these days.
Cartridges tossed into a fire or crushed will burst like low-grade fireworks once the primer is heated or deformed enough. The case almost always fails before the bullet ejects, and damage is minimal.
Ammunition can be reloaded to save money, for greater precision, for specific qualities, or when unavailable and not in production. The tools needed are fairly simple, and dies exist to shape a number of cases from existing blanks. Modern cartridges will fire in a vacuum; the oxidizer is in the propellant. Most military rounds are lacquered and will withstand considerable immersion in water. Firing underwater is not advised, due to increased pressure in the barrel.
Bullets follow a parabola when fired, as they are unpowered in flight. Unless the muzzle is pointed above plane, the bullet will only drop. Spun bullets precess slightly in flight, and the longer they are, the faster they must be spun for stability. Longer bullets tend to be more massive, but it is the length that matters, not the mass. If the bullet is supersonic, it will oscillate as it drops through transonic, and lose accuracy. Wind, rain, intervening material all affect accuracy.
Pretty much all modern bullets can be stopped by 6" of sandbag (the exception being a few heavy machine guns that are effectively light cannon). Modern rifles can shoot through cars, unless they hit an engine, transmission or differential. Much sentiment is bandied about regarding certain rounds "turning cover [barriers] into concealment," but it is largely sentiment. At moderate range (100 meters or less) most military rifles of any caliber will shoot through body armor unless it contains hard plates. Modern armor will stop most pistol rounds. However, soft armor will have backface deformation which can be up to 4" with some shotgun loads. This will cause critical injuries.
Bullets do not throw people back. Demonstrations exist that a .308 battle rifle at under a meter will move a person in armor a couple of centimeters. Any such reaction to being hit is neurological, not physical.
Bullets kill in four ways. By hitting the central nervous system - brain, brain stem. This is effectively instantaneous. They can hit critical organs - heart, liver, kidneys. This can take several seconds to several minutes. Trauma from energy applied to target is lethal if the cartridge is powerful enough, or if enough bullets hit. Finally, blood loss is fatal and may take seconds to hours.
The basics of firearm handling and safety can be taught in a few hours. It's not rocket science, and children are capable of learning supervised firearm handling before learning the balance necessary to ride a bike. Precision shooting depends on the individual and the type of shooting involved, from days to years.
Proper safety dictates that the first and last actions are to check the chamber, and to always unload a weapon before cleaning or maintaining. For mechanical tests, dummy cartridges and "snap caps" exist, or empty cases can be used.
Any machine shop with proper blueprints can build firearms in short order. A well-equipped garage can serve for slow production. Hand tools take longer, but it's been done. In the US, it is legal under federal law to manufacture a weapon for personal use, not commercial resale, as long as it complies with length and type restrictions. Registration is not required. States and cities have their own laws, however.
Various countries have various laws. Often, firearms before a given year - typically 1898-1900 - are exempt from regulation. Regulation may vary from licenses and taxes to prohibitions. Do your research. As with anything, there is a black market, but very few licensed dealers subject to inspections will go along with the cliché of selling to someone with "an honest face" without paperwork. The penalties include jail, loss of license, business and inventory. Likewise, no one buys a handgun in a gun store or pawn shop in Chicago, for example. Handguns are prohibited there (this is being challenged legally as of this writing). Using these clichés will cause your knowledgeable readers to throw the book across the room. Online sales must be transferred through a dealer. Dealer sales at a gun show, as at a store, are run through the NICS system (National Instant Criminal Background Check System), despite what may be reported elsewhere. Face to face sales between private citizens making occasional personal sales are permissible within state, but the state may have additional requirements. Again, criminal elements will do as they wish, but legitimate buyers and sellers will abide by the law. Be prepared to justify your story.
Currently, 48 US states have some provision for personal open or concealed carry of firearms. Rifles and shotguns are generally easier to carry, though hunting laws come into play even for non-hunters. Rural and agricultural states tend to be more lenient.
Generally, criminals tend to prefer readily available and concealable firearms - about what armed citizens and police carry. Assault rifles and machine guns are expensive, bulky and not very discreet or useful for holdups, and are thus very rarely used in crime.
Currently, good rifles start at $70 for surplus Russian Mosin Nagant 91/30s. Shotguns range from $70 for used single shots. The high end of both can run to tens of thousands for custom target or hunting guns. Junk handguns start at $70. Reliable ones run used from $150 on up. Does your character know which ones are good? What resources does he have for buying, and what time frame does he have?
This is a quick and general overview that doesn't go into detail about such things as the Webley-Fosbery Automatic Revolver and other devices that violate the standard rules. Pretty much anything can, and has, been done, but what I've covered here is the basics. Hopefully, this will make plotting and rough drafting easier, and give leads on what type of research to do. Remember that gun geeks are as knowledgeable and obsessive as physics or law geeks, and will mercilessly shred your story if you assume no one will notice. I've watched a ten page thread debating the physics of a rifle bullet from chamber to target, accounting for wind drift, velocity change, rotational effects and how casting temperature might affect the balance of the projectile.
You have been warned.
Some useful fora for additional research:
Gunbroker.com - Current prices for anything being sold.
Survivalblog.com - I am editor-at-large on this forum.
TheBoxOTruth.com - Actual tests of various weapons and various materials.
There are a huge number of "FirearmName.net" and "caliber.net" sites for fans of various weapons.
Good luck, and good shooting, at least on paper.