AR Spec Reference
The specs that decide whether two parts actually fit together. Counts are taken from the live parts catalog, so they reflect what's on the market — not what a forum post from 2013 says.
Muzzle thread pitch by caliber
The most common ordering mistake: a muzzle device that won't thread on. 1/2x28 is the .223/5.56 standard and 5/8x24 is the .30-caliber standard — they are not interchangeable. Big-bore and pistol calibers vary.
| Caliber | Platform | Thread pitch offered |
|---|---|---|
| .243 Win | AR-10 | 5/8x243 |
| .260 Rem | AR-10 | 5/8x243 |
| .308 Win / 7.62 | AR-10 | 5/8x2430 |
| .338 Federal | AR-10 | 5/8x243 |
| 6.5 Creedmoor | AR-10 | 5/8x2423 |
| .224 Valkyrie | AR-15 | 1/2x289 |
| .300 BLK | AR-15 | 5/8x2420 |
| .350 Legend | AR-15 | 1/2x2845/8x241 |
| .450 Bushmaster | AR-15 | 11/16x244 |
| .458 SOCOM | AR-15 | 5/8x244 |
| 5.56 NATO | AR-15 | 1/2x2887 |
| 6.5 Grendel | AR-15 | 5/8x2412 |
| 6mm ARC | AR-15 | 5/8x249 |
| 7.62x39 | AR-15 | 5/8x244 |
| .40 S&W | AR-9 | 9/16x241 |
| .45 ACP | AR-9 | .578x28111/16x241 |
| 10mm Auto | AR-9 | 9/16x242 |
| 9mm Luger | AR-9 | 1/2x2815 |
Counts are the number of barrels in the catalog offering that thread.
Gas system lengths
Gas length must match between barrel and gas tube — they are physically different lengths. Longer systems run at lower port pressure with a longer dwell time, which means a softer impulse and less wear.
| System | Port to chamber | Typical barrels | Notes |
|---|---|---|---|
| Pistol | ~4" | 7–10.5" | Highest port pressure and the harshest impulse; used only where a barrel is too short for anything else. |
| Carbine | ~7" | 10–16" | The M4 standard. Reliable and common, but sharper recoil than mid-length on a 16" barrel. |
| Mid-length | ~9" | 14–20" | Preferred on a 16" barrel — lower port pressure, longer dwell, noticeably softer cycle. |
| Rifle | ~12" | 18–20"+ | Softest-shooting and easiest on parts; requires the barrel length to support it. |
In the catalog right now: rifle96mid61carbine41pistol18
Barrel twist vs. bullet weight (.224 bore)
Twist rate determines how fast the bullet spins, and heavier bullets need more spin to stabilize. Too slow a twist for your ammo shows up as poor accuracy and oval "keyhole" holes in paper.
| Twist | Stabilizes | Notes |
|---|---|---|
| 1:12 | 40–55 gr | Old .223 standard. Will not stabilize modern heavy bullets. |
| 1:9 | 40–69 gr | Common budget spec. Frequently fails to stabilize 75–77 gr. |
| 1:8 | 40–77 gr | The best all-rounder — handles nearly the full commercial range. |
| 1:7 | 55–90 gr | Military spec. Stabilizes everything heavy; slight overspin on very light bullets. |
All twists in the catalog (all calibers): 1:8941:7591:10511:7.591:1691:2441:1441:6.52
Buffer weights
Buffer mass tunes the bolt-carrier cycle. Over-gassed or suppressed rifles generally want more mass; under-gassed rifles want less.
| Buffer | Weight (oz) | Typical use |
|---|---|---|
| Carbine | 3.0 | Standard carbine buffer. Baseline for a mid-length or rifle-gas 16" build. |
| H (H1) | 3.8 | One tungsten weight. Common fix for over-gassed carbines. |
| H2 | 4.6–4.7 | Two tungsten weights. Typical for short-barreled or suppressed builds. |
| H3 | 5.0–5.4 | Three tungsten weights. Heavy suppressed and over-gassed setups. |
| Rifle | 5.0–5.2 | Rifle-length buffer — only fits a rifle-length receiver extension. |
| 9mm / blowback | 5.0–8.0 | PCC-specific. Blowback needs the extra reciprocating mass to stay timed. |
Receiver extension compatibility
Buffer tube, buffer, spring, and stock have to belong to the same system. Mixing lengths here is one of the most common build-stopping mistakes.
| Receiver extension | Buffer | Spring | Stock | Notes |
|---|---|---|---|---|
| Carbine (6-position) | Carbine / H / H2 / H3 | Carbine | Collapsible | The most common AR-15 configuration. |
| Rifle (A2, fixed) | Rifle | Rifle | Fixed A1/A2 | Longer tube and spring; will not accept a collapsible stock. |
| A5 (VLTOR) | A5-specific (A5H0–A5H4) | Rifle-length | Collapsible | Carbine-diameter tube with rifle-length spring travel — needs dedicated A5 buffers. |
| Pistol | Carbine | Carbine | Brace only | Not designed to mount a shoulder stock. |
The builder checks every one of these automatically as you pick parts.
Open the build planner →Related: caliber comparison · barrel length guide · first build guide
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Legal & safety disclaimers (read me)
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ArmoryBench is a free, informational planning and visualization sandbox. You use it to experiment with hypothetical AR-15/AR-10 configurations — nothing more. There is no cart, no checkout, no inventory, and no way to buy anything here. We do not sell, offer for sale, ship, transfer, broker, or facilitate the sale of any firearm, receiver/frame, part, accessory, or NFA item. Any purchase must be made separately through the actual manufacturer or a licensed dealer.
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Part specs, weights, prices, compatibility results, reviews, and availability are best-effort estimates and community-sourced information that may be incomplete, outdated, or wrong. They are provided "as is," without warranty of any kind. This is not legal, engineering, gunsmithing, or safety advice. Independently verify all specs, compatibility, and current law with the manufacturer and a qualified professional before buying, assembling, or firing anything. You are solely responsible for how you use this information.
Pricing
All prices shown are approximate MSRP (manufacturer suggested retail) for reference only — ArmoryBench does not sell parts. Street prices are often lower, so always check current pricing and shop around; you can frequently find sales and better deals from reputable retailers.
Sound Is Ranked, Not Measured
ArmoryBench does not publish decibel levels. A 2026 review of published suppressor data found that most manufacturers release either nothing at all or bare numbers without the test standard, weighting, and microphone position needed to compare one against another — and that most cartridges have no published unsuppressed reference level whatsoever. Rather than present figures assembled from sources like that, we show a relative ranking: how loud one configuration is likely to be next to another, and how much to trust that comparison.
These rankings are algorithmic approximations for educational purposes only. They are not laboratory measurements and are no substitute for professional acoustic testing or OSHA/NIOSH occupational noise guidance. Peer-reviewed testing has found no suppressed centerfire rifle configuration reliably below the hearing damage threshold at the shooter’s ear. Always use proper hearing protection when firing any firearm, suppressed or not.
Ballistic Coefficients
Where a manufacturer publishes a ballistic coefficient we use it. Most hunting, defensive, and house-brand loads don't publish one, so those use a value typical of the bullet's construction, flagged as an estimate wherever it appears. Be aware that advertised BCs often run optimistic — some bullets measure meaningfully lower in the field than on the box, and the gap widens past roughly 600 yards as the bullet slows. Treat every trajectory here as a starting point for confirming on paper, not a substitute for it.
Exterior Ballistics
Trajectory, drop, wind drift, and energy figures are computed estimates based on a standard point-mass ballistic model and the inputs you supply. Actual performance varies with atmospheric conditions, chronograph accuracy, and firearm/ammunition variance. Verify zero and trajectory data at the range before hunting or competition use.
Reloading Data
This tool does not calculate chamber pressure and never generates a charge weight from first principles. Any future custom-load feature is constrained to interpolation between published load-data points and must never be the sole basis for a handload. Always verify any load against current published data from the powder and bullet manufacturer, start at the published starting load, and never exceed a published maximum charge.
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This app does not sell, ship, or transfer firearms, receivers/frames, or NFA-regulated items. It is a research and planning tool only. All purchases of receivers, frames, or complete firearms must be completed through a licensed Federal Firearms Licensee (FFL).
NFA Items
Configurations involving suppressors, or a barrel under 16" paired with a shoulder stock (SBR), require ATF approval (Form 1 or Form 4), a background check, and an approval wait period before assembly or possession. As of January 1, 2026, the associated $200 federal tax was eliminated by federal law; the registration, background-check, and approval process itself was not eliminated and remains fully in effect. Verify current law in your jurisdiction — you are solely responsible for completing all required legal steps.
Your Responsibility
Building or modifying a firearm carries legal and safety obligations that vary by federal, state, and local law. You alone are responsible for ensuring any configuration you build is legal where you live and is assembled safely. To the fullest extent permitted by law, ArmoryBench and its authors disclaim all liability for any decision, purchase, assembly, or outcome arising from use of this tool.