Reference
Firearm & Ammunition Glossary
Buying your first firearm comes with a wall of acronyms and shorthand — FFL, NFA, MOA, FMJ, grain. This is a plain-English glossary of the 38 terms a new or intermediate owner runs into most, written to be accurate and neutral. Use it to decode a listing, a forum thread, or a conversation at the counter.
Buying, selling & the law
The terms that come up most when transferring a firearm legally.
- FFL (Federal Firearms License)
- A license issued by the ATF that allows a business or individual to manufacture, import, or deal in firearms. In everyday use, “an FFL” usually means a licensed dealer who can legally receive a firearm shipment, run a background check, and complete a transfer. Any sale shipped across state lines must go through an FFL on the receiving end.
- FFL transfer
- The process of routing a firearm through a licensed dealer so the buyer can complete a Form 4473 and background check before taking possession. Online and out-of-state purchases are shipped to the buyer’s chosen FFL, who hands the firearm over only after the check clears (plus any state waiting period).
- NICS (National Instant Criminal Background Check System)
- The FBI system a dealer queries to determine whether a buyer is legally allowed to receive a firearm. A check returns Proceed, Delay, or Denied. Most checks finish in minutes; a Delay can take up to three business days.
- Form 4473
- The ATF Firearms Transaction Record a buyer completes at a dealer for every over-the-counter purchase. It captures identity details and asks eligibility questions; knowingly answering falsely is a federal crime.
- Universal background check
- A state-level requirement that private, person-to-person sales also go through a licensed dealer for a background check — not just purchases from a store. Federal law does not mandate this nationwide, so whether it applies depends on your state.
- Private sale
- A transfer between two private individuals rather than through a dealer. Federal law still bars selling to anyone you know or have reason to believe is prohibited, and many states layer on additional rules such as a required background check.
- Straw purchase
- Buying a firearm on behalf of someone who is prohibited from owning one, or who wants to hide that they are the true buyer. It is a serious federal felony — lying on the Form 4473 about being the “actual buyer” is the most common way it is charged.
- Prohibited person
- Someone federal or state law bars from possessing firearms — for example, certain felony convictions, specific domestic-violence findings, or an adjudication as mentally incompetent. Selling or transferring to a prohibited person is illegal even in a private sale.
- Waiting period
- A state-imposed delay between purchase and taking possession of a firearm. Some states have none; others require several days. It is separate from a NICS Delay, and both must clear before transfer where they apply.
- C&R (Curio & Relic)
- A category for firearms of special interest to collectors — generally those at least 50 years old or certified as collectible. A Type 03 C&R license lets collectors receive qualifying firearms directly, subject to state law.
NFA & regulated items
Items regulated under the National Firearms Act, which adds federal registration and tax steps.
- NFA (National Firearms Act)
- A 1934 federal law regulating a specific class of items — suppressors, short-barreled rifles and shotguns, machine guns, and “any other weapons.” Acquiring NFA items requires ATF registration, an approved application, and a federal tax stamp.
- Tax stamp
- Proof of the federal transfer tax (commonly $200) paid when registering an NFA item such as a suppressor or short-barreled rifle. The approved application and stamp must exist before you take possession.
- SBR (Short-Barreled Rifle)
- A rifle with a barrel under 16 inches or an overall length under 26 inches. SBRs are NFA-regulated, so building or owning one legally requires ATF approval and a tax stamp. Configuration rules are strict — details matter.
- SBS (Short-Barreled Shotgun)
- A shotgun with a barrel under 18 inches or an overall length under 26 inches. Like the SBR, it is an NFA item requiring registration and a tax stamp.
- Suppressor (silencer)
- A muzzle device that reduces a firearm’s report and muzzle flash. It does not make a gun “silent.” Suppressors are NFA-regulated, legal to own in most states with the proper registration and tax stamp, and banned in a few.
- AOW (Any Other Weapon)
- An NFA catch-all for concealable or unconventional firearms that don’t fit the rifle, shotgun, or handgun categories — such as certain pen guns or smooth-bore pistols. Transfers carry a reduced federal tax.
Firearm types & platforms
How firearms are categorized by action, format, and design family.
- Semi-automatic
- A firearm that fires one round per trigger pull and automatically chambers the next from the magazine. This is the most common action for modern handguns and many rifles. It is distinct from fully automatic fire.
- Bolt-action
- A manually operated action where the shooter lifts and pulls a bolt to eject the spent case and chamber a fresh round. Prized for accuracy and reliability, it is common on hunting and precision rifles.
- AR platform
- A family of modular semi-automatic rifles based on the AR-15 design (“AR” stands for ArmaLite, the original maker — not “assault rifle”). Known for interchangeable parts and customization, commonly chambered in 5.56 NATO / .223.
- AK platform
- A family of rifles derived from the Kalashnikov design, valued for rugged reliability and commonly chambered in 7.62×39mm. AR and AK are different design lineages, not better-or-worse versions of the same gun.
- Striker-fired
- A handgun design in which a spring-loaded striker, rather than an external hammer, ignites the cartridge. It enables a consistent trigger pull and a snag-free profile, and is the norm for many modern carry pistols.
- Receiver / frame
- The serialized core of a firearm — the part legally considered “the firearm” and stamped with a serial number. “Receiver” is typical for rifles and “frame” for handguns. Transfers and background checks attach to this part.
Ammunition & ballistics
What the numbers and letters on an ammo box actually mean.
- Caliber
- The internal diameter of a barrel’s bore, and by extension the size of cartridge it fires — expressed in inches (.45, .308) or millimeters (9mm). A firearm is chambered for a specific cartridge; using the wrong one is dangerous.
- Cartridge (round)
- A complete unit of ammunition: case, primer, powder, and bullet. “Round” is the everyday synonym. The bullet is only the projectile — the part that leaves the barrel — not the whole cartridge.
- Magazine vs. clip
- A magazine is the spring-loaded device that feeds cartridges into the firearm's action (where the bolt or slide then chambers them), often detachable. A clip merely holds rounds together to load a magazine or fixed cylinder. The two are not interchangeable, though “clip” is often used loosely.
- Large-capacity magazine (LCM)
- A magazine holding more than a state-defined limit — frequently 10 or 15 rounds where limits exist. Capacity restrictions vary widely by state, so a magazine legal in one place may be restricted in another.
- FMJ (Full Metal Jacket)
- A bullet whose soft lead core is encased in a harder metal jacket. FMJ rounds resist deformation, feed reliably, and are common for target practice and training.
- HP (Hollow Point)
- A bullet with a hollowed tip designed to expand on impact, transferring energy and limiting over-penetration. It is a common choice for self-defense and is restricted in a small number of jurisdictions.
- Grain (gr)
- A unit of weight (1/7,000 of a pound) used to describe bullet and powder mass. A heavier-grain bullet generally travels slower with more momentum; a lighter one, faster and flatter. It is a weight, not a measure of power.
- Muzzle velocity
- The speed of a bullet as it leaves the barrel, measured in feet per second (fps). It influences trajectory and energy and varies with caliber, bullet weight, and barrel length.
- Centerfire / rimfire
- Two primer types. Centerfire cartridges have the primer in the center of the case base and are reloadable and more powerful; rimfire (like .22 LR) has the priming compound in the rim and is inexpensive but not reloadable.
Accuracy, optics & maintenance
Terms you’ll meet at the range and the cleaning bench.
- MOA (Minute of Angle)
- An angular measurement of accuracy and scope adjustment. One MOA spans roughly 1 inch at 100 yards (and grows proportionally with distance). A rifle that shoots “1 MOA” groups about 1 inch at that range.
- Zero / sighting in
- Adjusting sights or an optic so the point of aim matches the point of impact at a chosen distance — for example, a “50-yard zero.” A firearm is sighted in before it can be expected to hit where it is aimed.
- Red dot / reflex sight
- A non-magnifying optic that projects an illuminated aiming dot onto a lens, allowing fast target acquisition with both eyes open. Common on handguns, carbines, and shotguns.
- Bore / chamber
- The bore is the hollow interior of the barrel the bullet travels through; the chamber is the section at its rear that holds the cartridge before firing. Both are key points to inspect and clean.
- Bore brush & patch
- Cleaning tools run through the barrel on a rod or pull-through. A bore brush scrubs fouling loose; a cloth patch carries solvent in and wipes residue out. Routine cleaning preserves accuracy and reliability.
- Fouling
- The carbon, copper, and lead residue that builds up in a barrel after firing. Excess fouling degrades accuracy over time, which is why barrels are cleaned with solvent and brushes.
- Dry firing
- Pulling the trigger on an empty chamber to practice trigger control and fundamentals without live ammunition. It is safe for most modern centerfire firearms but can damage some rimfire guns — check the manual.
General information, not legal advice. Definitions are simplified for clarity, and the rules that attach to many of these terms — especially NFA items, magazine capacity, and private sales — vary by state and change over time. Check your state’s firearm-law summary and consult a licensed attorney before any purchase, build, or transfer.
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