Gun Part Compatibility Checkers and AR-15 Calculators
Compatibility checkers, tuning calculators and legal length checks that end in parts you can actually buy. Every result is drawn from the live catalog and the parts people configure here, not from a static table.
Build planning tools
Price the build before the first part ships.3
ToolAR Build Cost Calculator
How much does it cost to build an AR-15? Pick caliber, barrel length, stock or brace and optic, then drag both edges of the price band from the cheap end to the top end. Every slot fills with the part builders add most that is in stock, priced live. The headline total is the core rifle, optics and extras are priced separately, and beside them sits what builders really pay per slot, measured from real part picks. Roll a random build, or open yours in the builder in one click. Computed from over 1 million AR parts selected on GunPartPicker since 2020.
ToolGun Paint Planner
Rattle can guns online before you spray. Paint, stencil and camo a real photo of about 1,800 guns: AR-15s, AR-10s, AR-9s, AKs, every Glock, pistols, shotguns and bolt action rifles, the way the rattlecanned guns on r/rattlecannedguns are done, with Krylon, Rust-Oleum, Aluma-Hyde, DuraCoat and Cerakote colors, then get the cans to buy in spray order.
ToolNight Vision
Look around a real 360 degree scene through Gen 1, Gen 2+, Gen 3 green and white phosphor tubes, digital night vision and thermal. Turn the moon down from full to overcast, switch on an IR light, compare two devices side by side. Or walk a 3D farm at night and spot the people, hogs and deer hiding in it. Then see the PVS-14, PVS-31, GPNVG-18 and the thermal scopes people buy, with prices.
Compatibility checkers
What fits what, checked against the parts we track.15
ToolMuzzle Thread Checker
Pick your barrel's caliber and platform, get the standard thread pitch, and see every muzzle device and suppressor in the catalog that actually threads on, with live prices.
ToolSuppressor Mounts (3D)
Put a can on its mount in 3D. Compare SilencerCo ASR, Dead Air KeyMo, SureFire Fast-Attach, HUXWRX QD, HUB 1.375x24 and direct thread: what goes on the barrel, what is on the can, how it locks and which cans fit which mounts. Cut it open to see the taper and the baffles, then shop the mounts and cans in stock.
ToolDI vs Piston (3D)
Watch a direct impingement AR-15 and a gas piston HK416 fire in slow motion x-ray 3D. Follow the gas from the port back into the carrier, or into a piston that kicks an op rod, see which bolt runs hot, and compare weight, cleaning, suppressed use, carrier tilt and cost.
ToolUpper vs Lower Receiver (3D)
Take a real AR-15 apart in 3D and see how the upper and lower receiver go together. Push the takedown pin, hinge the upper open on the pivot pin, pull the bolt carrier group and lift the upper off, with every part colored by the half it belongs to.
ToolHow Muzzle Devices Work (3D)
Watch one shot leave an AR-15 muzzle in slow motion 3D through a bare barrel, a flash hider, a compensator, a muzzle brake and a linear comp. See where each sends the gas, and what that does to flash, recoil, muzzle rise and the blast beside you.
ToolHow a BCG Works (3D)
Watch an AR-15 bolt carrier group unlock, extract and lock again in slow motion 3D, then take it apart part by part. See the cam pin turn the bolt out of the barrel extension, and what each part does.
ToolBuffer Tube and Stock (3D)
See an AR-15 buffer tube, end plate, castle nut and stock go on in 3D, walk the stock through its six positions, and put a mil spec and a commercial tube side by side to see why a stock only fits one of them.
ToolHow a Charging Handle Works (3D)
Watch an AR-15 charging handle unlatch and pull the bolt carrier back by its gas key in 3D, then watch the rifle fire while the handle stays put. Compare a standard latch with an ambidextrous one.
ToolHow the Gas System Works (3D)
Watch a shot's gas go up an AR-15's gas port, through the gas block and back down the gas tube to the bolt carrier in slow motion 3D. Turn it down with an adjustable gas block, and see where the port sits on pistol, carbine, mid length and rifle gas.
ToolFree Float vs Drop In Handguard (3D)
Watch an AR-15 free float handguard go on its barrel nut in 3D, lean on a free float and a drop in handguard to see which one moves the barrel, and lock an M-LOK rail section in. Plus M-LOK vs KeyMod and what length fits your barrel.
ToolHow Triggers Work (3D)
Watch a standard trigger, a forced reset trigger and a binary trigger run inside an x-ray AR-15 in slow motion 3D. See the hammer, the disconnector, the FRT's locking bar and the bolt carrier at every step, and what each one needs and where it is legal.
ToolFRT and Binary Trigger Picker
Choose your platform and see every forced reset trigger, binary trigger and Super Safety the catalog carries for it, what the host needs to run one, and where each is in stock.
ToolGlock Red Dot Fit Checker
Pick how your Glock slide is cut and see which red dots mount directly, which need a plate, and the plates and optics in stock right now.
ToolGlock Size Comparison
Pick any two Glocks and see them to scale as real photos sized to Glock's published dimensions, side by side, from behind and as an X-ray, with the difference in length, height, width and weight in one line and the pistols in stock for each.
ToolP385 Size Comparison
See the SIG P385 CARRY, COMP and FULL to scale against the P365-XMACRO, the P320 and the Glock 19, 17, 45 and 43X, as real photos sized to the published length and height, with every dimension and where to order one.
Tuning calculators
The numbers behind a gun that runs.4
ToolTwist Rate Calculator
Pick a bullet and a twist rate, get the Miller stability factor, then see barrels with that twist and ammo loaded with that bullet, with today's price per round.
ToolOptic Zero (3D)
See where a 25, 36, 50, 100 or 200 yard zero hits on a 3D range, with your ammo, barrel length and optic height. Compare two zeros side by side, look through your red dot, EOTech or LPVO at each distance, then tap where your group hit and get the exact clicks up, down, left and right for your optic.
ToolBuffer Weight Calculator
Enter your gas system, barrel length, buffer tube and ammo, add a suppressor or a fast trigger, and get the buffer weight to start with plus the buffers in stock that match.
ToolBuffer System (3D)
Watch an AR-15 cycle in slow motion, cut open: gas drives the bolt carrier back, the bolt unlocks and throws the brass, the buffer and spring soak it up and send it home. Swap carbine, H, H2 and H3 buffers, add gas or a suppressor, and see the carrier speed, where the brass lands and when it short strokes.
Legal length checks
Where the federal lines are before you build.3
ToolGun Travel Checker
Can I bring my gun to another state? Pick where you start, where you are going and what is coming along: carry pistol, AR-15, magazines, suppressor, SBR, brace, forced reset or binary trigger, hollow points. Every state on the route is checked for transporting firearms across state lines: magazine limits, assault weapon bans, NFA rules, carry permit type and trigger bans, with what to do before the state line.
ToolBarrel and Overall Length Checker
Enter barrel length, muzzle device and how the back end is configured, and see whether the build is a rifle, a short barreled rifle, a pistol or an AOW under federal law, with the barrels in stock at that length.
ToolSBR Planner (3D)
Set the barrel anywhere from 7.5 to 16 inches, put a stock, a brace or a folder on the back, pin a muzzle device or slide on a can. The ruler under the rifle shows whether you've cleared the 16 inch barrel line and the 26 inch overall line. Pick your state for its SBR, suppressor and assault weapon rules, then price every part and open the build in one click.
Already on the site
- AR-15, AR-10 and AR-9 Builders with compatibility checks on every slot
- Glock Builder model, generation and cut aware
- Ammo Finder cost per round, refreshed daily
- Gun Laws by State all 50 states, ten rules each