Building and Buying an AR-15

The AR-15 has been the most common centerfire rifle sold in America for two decades, and the market reflects it. You can buy a complete rifle for a few hundred dollars or spend five times that on parts alone. Both paths work. What separates a rifle that runs from one that frustrates you is not the price tag but a short list of specifications that actually change how the gun behaves. This guide covers those, and then covers what it really costs to build one yourself.

Buy complete or build from parts

A complete rifle from a manufacturer arrives headspaced, staked, function-tested and warrantied. If something breaks, one company owns the problem. That is worth a great deal to a first-time buyer, and it is why most people should start there. We stock complete rifles from a wide range of makers, including Ruger, Smith and Wesson, Daniel Defense, Aero Precision, Radical Firearms and others, and we treat them all the same way: as one brand among many on the shelf.

Building from parts makes sense when you want something the factory does not offer, when you already own a lower, or when you enjoy the work. It rarely saves money on a first rifle once you count the tools. A vice block, an armourer's wrench, a torque wrench, punches and a headspace-safe way to check your work add up. Building the lower is genuinely easy and needs almost no special tooling. Building an upper properly is where the real skill sits, which is why plenty of experienced builders assemble their own lowers and buy complete uppers.

The specifications that matter

Barrel length and gas system

Barrel length and gas system length have to match. A sixteen-inch barrel with a mid-length gas system is the most forgiving combination in the catalogue and the one we recommend to most buyers. It softens recoil, runs a wide range of ammunition, and tolerates a suppressor or a dirty bolt better than a carbine-length system on the same barrel. Fourteen-and-a-half-inch barrels with a pinned and welded muzzle device get you to the same legal length with a shorter profile. Eighteen and twenty-inch rifle-gas guns are smoother still and better for precision work, at the cost of handling indoors.

Barrel steel, profile and twist

Chrome-moly vanadium steel with a chrome-lined or nitrided bore lasts longest under volume fire. Stainless barrels usually shoot tighter groups and wear faster. Profile is about balance more than accuracy: a government profile barrel is a compromise nobody designed on purpose, a pencil profile handles beautifully and heats up quickly, and a heavy profile is steady on a bipod and tiring offhand. Twist rate decides what bullets stabilise. A 1:7 twist handles everything from 55 to 77 grains and is the safest default. A 1:8 is an excellent all-rounder. A 1:9 struggles with the heaviest match bullets.

Chamber

Buy a 5.56 NATO or .223 Wylde chamber, not a .223 Remington chamber, unless you know you will only ever shoot .223. A 5.56 chamber shoots both safely. A .223 chamber is not rated for 5.56 pressures.

Bolt carrier group and the small parts

This is where a cheap rifle shows itself. Look for a properly staked gas key, a shot-peened and magnetic-particle-inspected bolt, and a carrier of the right weight for your gas system. A correctly staked key costs nothing extra from a good maker and is the single most common failure point on a bargain build.

Trigger

A standard mil-spec trigger breaks somewhere between five and eight pounds with noticeable grit. A drop-in cassette trigger in the three-to-four-pound range is the cheapest meaningful upgrade you can make to any AR, and it takes about five minutes to install. Single-stage triggers suit defensive and general use, two-stage triggers suit precision work. We also stock forced-reset and binary units, which are a different category of part with their own legal considerations covered in the trigger guide.

Calibres beyond 5.56

The AR platform swaps calibre by changing the upper, and sometimes the magazine and bolt. The choice is usually driven by hunting law. Several states restrict deer hunting to straight-wall cartridges, which is why .350 Legend and .450 Bushmaster exist and sell well. Where any centerfire is legal, 6.5 Grendel and .308 Winchester in an AR-10 pattern rifle cover deer cleanly at range. .300 Blackout is a short-barrel and suppressor calibre that also works well on hogs inside 150 yards, and it uses standard 5.56 magazines and bolts. Check your own state's rules on the city pages before you choose, because the legal calibre list changes across a state line.

Sighting the rifle

For general purpose and defensive use, a quality red dot on a lower-third co-witness mount with backup iron sights is hard to beat. For a rifle that has to identify and hit targets past 200 yards, a low-power variable optic in one-to-six or one-to-ten power does both jobs with a small weight penalty. Budget roughly a third of what you spent on the rifle for the optic and mount, and do not save money on the mount. A drifting mount destroys the value of an expensive optic.

Magazines, ammunition and consumables

Buy magazines in quantity from a known maker and treat them as consumables. Load ammunition in two tiers: cheap brass-cased 55 grain for volume practice, and a defensive or hunting load you have actually zeroed and confirmed. Keep a spare bolt, a spare extractor spring with its insert, a spare gas ring set and a spare firing pin in your range bag. Those four parts cover the overwhelming majority of stoppages that are not magazine related.

A sensible first build

Complete lower receiver from a known maker, or a stripped lower and a quality lower parts kit
Complete sixteen-inch mid-length upper, 5.56 or .223 Wylde chamber, 1:7 or 1:8 twist, nitrided bore
Bolt carrier group with a staked gas key and an MPI-tested bolt
Three-to-four-pound drop-in trigger
Red dot with a solid mount and folding backup irons
Ten good magazines, a sling and a weapon light

That combination costs less than most people expect, runs reliably, and leaves nothing important to upgrade later except the optic. Everything on the list is in the shop, and the rifle itself ships to the dealer you choose. If you are unsure whether a given configuration can ship to your address, read the rules for your state on the state gun laws overview or your own city page first, because magazine and feature limits in a few states decide the answer.

General information, not legal advice. Current as of September 2026. Laws change; check the official source before you act.