AR-15 Upgrades by Setup: Pistol, 14.5, 16 Inch, 300 Blackout and Factory Rifles

What you should upgrade first depends on the rifle you have. Builders on 11.5 inch and shorter barrels reach for braces and brakes, 14.5 inch builders pick holographic sights more than half the time, 16 inch builders keep an $11 A2 flash hider, and 18 inch builders add scopes.

The short answer

The three upgrades builders make most are a trigger, a stock and an optic. Builds made from a complete upper and lower replace the trigger 53% of the time and the stock 43%, and owners of factory rifles add an optic before anything else. Here's the most picked of each under $100 at today's prices.

Best trigger under $100: ALG Defense QMS, $63.16 today. A mil-spec single stage with honed sear surfaces, so it feels smoother than a factory trigger.

Best stock under $50: Magpul MOE carbine stock, $33.99 today. It's the most picked stock on 16 inch builds, at 23% of stock picks.

Best red dot under $100: SIG Romeo 5 Gen II, $99.99 today. A 2 MOA dot that SIG rates at up to 40,000 hours on one battery.

Pick your setup

Attach rates by barrel length

Find your column to see how your setup compares. Each cell is the share of builds in that group that fill the slot, and you should read a bold difference as the signal, not the exact number.

Two patterns stand out. Long barrels trade dots for scopes, and 18 inch builders replace the handguard more than anyone. 300 Blackout builders add suppressors more than any other group, which makes sense for a cartridge built to run quiet.

16 inch rifles: the default build

More builds in our builder use a 16 inch barrel than any other length, and their upgrade list is the most conservative. Red dots take 52% of the optic slot, the most of any length, though the EOTech HHS is still the single most picked optic at 17%.

At the muzzle, 16 inch builders keep it cheap. The A2 flash hider leads at 18% of muzzle picks for about $11, and the KAK A1 is second at 10% for about $6. The Magpul MOE carbine stock takes 23% of stock picks, and the Streamlight ProTac HL-X with a laser takes 30% of light picks.

Our best AR-15 upgrades guide ranks the most picked part in every slot across all builds.

18 inches and longer: scopes and long rails

Builds with an 18 inch or longer barrel add a rifle scope 19% of the time, against 8% across all ARs, and they add a handguard 27% of the time, the most of any group. The 15 inch Midwest Industries Quad Rail leads their handguard picks at 18%.

If you're building one of these precision or marksman rifles, read our LPVO and rifle scope guides before you pick glass.

300 Blackout: built to run quiet

300 Blackout builders add a suppressor 31% of the time, and 81% of the cans they pick are 30 caliber, against 33% across all ARs. The SilencerCo Omega 300 leads at 15% of their suppressor picks. Braces take 17% of the stock slot on 300 Blackout builds, and brakes take 65% of their muzzle devices.

Our best 300 Blackout suppressors guide ranks the cans, and 300 Blackout vs 5.56 covers whether the cartridge suits you.

AR-9 and AR-10

9mm AR builders who add a suppressor pick a pistol caliber can 51% of the time. Our best AR-9 upgrades guide ranks their parts. AR-10 and .308 builders add a rifle scope 20% of the time, and best AR-10 upgrades covers that platform.

Factory rifle owners accessorize

If you own a factory rifle, you'll probably buy accessories before parts, because the rifle already has its internal parts. Owners who start a build from a complete rifle add an optic 44% of the time, a suppressor 34% and a light 25%.

The rifle's price predicts the suppressor. Owners of rifles under $750 add one 24% of the time, and owners of rifles at $1,500 or more add one 52% of the time. Optic rates barely move with price, but the optic's price does. The $1,289 EOTech HHS takes 22% of optic picks among owners of rifles at $1,500 or more, against 13% among owners of rifles under $750.

The two factory rifles with their own guides are the S&W M&P15 Sport III and the PSA PA-15.

Upgrades under $100 that lead their slots

Each part below is the most picked part in its slot under the price shown, checked against today's prices. Where a price moved, we used today's: the Rise Super Sporting trigger was picked at a median of $98 but costs $108 now, so the ALG Defense QMS takes the trigger spot.

ALG Defense QMS: best trigger under $100

What we like

• Honed sear surfaces give a smoother pull than a factory trigger, at about 6.5 pounds.
• It's $63.16 today, about a fifth of a Geissele SSA-E X.

Watch out for

• It doesn't get lighter. If you want a light, crisp pull, our trigger guide covers the drop in triggers that cost more.

Magpul MOE carbine stock: best stock under $50

What we like

• It's $33.99 today, and ten of the stores we track have it.
• It leads the stock slot on 16 inch builds at 23%, so it's the stock you'll see on more rifles than any other.

Watch out for

• This version fits mil-spec diameter buffer tubes. A commercial diameter tube needs Magpul's commercial version.

SIG Romeo 5 Gen II: best red dot under $100

What we like

• A 2 MOA dot with motion activation, rated at up to 40,000 hours on one CR2032 battery.
• Ten of the stores we track have it in stock today.

Watch out for

• It sits right on the line at $99.99. Builders picked it at a median of $110, so a small price rise puts it back over $100.

Every slot under $100

Where the forums and builders disagree

Instructors and forum regulars put a sling near the top of every beginner list, next to an optic and a light. Our builder has no sling slot, so slings never show up in these numbers, and that's a gap in the data, not proof that builders skip them.

How we pick

We read the final parts list of each GunPartPicker AR build, sort builds by barrel length and caliber, and report each part's share of its slot, so a part only counts if it's still in the build at the end. A price marked today is the live price when we last updated this guide, and a price builders picked at is the median they paid. The cards show the current price at the stores we track.

What to read next

• AR pistol upgrades for builds 11.5 inches and shorter.
• 14.5 pin and weld upgrades for M4 length builds.
• M&P15 upgrades and PA-15 upgrades for the two most popular factory rifles.
• Best AR-15 upgrades for the most picked part in every slot.