Does the Stern Defense SD 4in MOD4 M-LOK 4in work with the FailZero AR9?

Stern Defense SD 4in Mod4 M-Lok 4in Barrel 9mm Black Complete Upper Receiver Black SDINBRLKK

Upper Receiver

Stern Defense SD 4in MOD4 M-LOK 4in Barrel 9mm SDINBRLKK

from $419.27

FailZero AR9, 9mm BCG, Black Nitride

Bolt Carrier Group

FailZero AR9

from $132.03

Stern Defense upper and FailZero bolt carrier group compatibility

Yes, they fit

The Stern Defense SD 4in MOD4 M-LOK 4in Barrel 9mm works with the FailZero AR9. Our compatibility rules found no conflict between them.

Checked by the same rules the AR builder runs on every part you add: caliber, frame size, receiver pattern, thread pitch and gas length.

Fit is judged from the specs retailers list, which can be missing or wrong. Confirm with the manufacturer before you buy, and have a qualified gunsmith check any build before you fire it.

How often builders pair the Stern Defense upper and FailZero bolt carrier group

Backed by thousands of qualified builds that have both an upper and a bolt carrier group.

Bolt Carrier Groups builders put on the Stern Defense SD 4in MOD4 M-LOK 4in

Share of builds with the Stern Defense SD 4in MOD4 M-LOK 4in and any bolt carrier group

Upper Receivers builders put under the FailZero AR9

Share of builds with the FailZero AR9 and any upper

  • Stern Defense SD 4in MOD4 M-LOK 4in

    Of upper picks
    0%
    Median paid
    $419

  • FailZero AR9

    Of bolt carrier group picks
    0.3%
    Median paid
    $131
How we count ⌄

These shares come from GunPartPicker's build data: real parts lists people put together while planning a purchase, not sales or surveys. A build counts a part only when it is the final pick for its slot, so parts that were swapped out never count. Fit never comes from these numbers; it comes from our compatibility rules alone.

Frequently built with the Stern Defense upper and FailZero bolt carrier group

The part builders pick most often in each slot alongside these two, checked against both. Parts that conflict are left out.

Charging Handle

Trigger

Pistol Grip

Lower Receiver

Stock & Brace

Suppressor

Optic

Barrel

Handguard

Stern Defense SD 4in MOD4 vs FailZero AR9: specs and prices

Stern Defense SD 4in MOD4FailZero AR9
Best price$419.27 at Optics Planet$132.03 at BattleHawk Armory
Stores1 of 1 in stock4 of 4 in stock
AssemblyCompleten/a
PlatformAR-9n/a
Caliber9mmn/a
Length4n/a
Cartridgen/a9mm
Stylen/aPistol Caliber Blow Back Carrier
Finishn/aNitride

Both for $551.30 at today's best prices.

Today's best prices and 90 day price history

Every store we track for each part, cheapest in stock first. Prices are checked through the day.

Stern Defense SD 4in MOD4 M-LOK 4in Barrel 9mm

FailZero AR9

Price history, last 90 days

  • Stern Defense SD 4in MOD4 M-LOK 4in: lowest $376.96 on Jul 5, highest $419.27 on Jul 12 over the last 90 days.
  • FailZero AR9: lowest $132.03 on Jul 5, highest $179.99 on Aug 28 over the last 90 days.

Bolt Carrier Groups most paired with Stern Defense uppers

The Stern Defense SD 4in MOD4 M-LOK 4in is not in enough builds yet, so these are the most picked next to any Stern Defense upper. Only parts our rules say fit the Stern Defense SD 4in MOD4 M-LOK 4in are listed.

Upper Receivers frequently paired with the FailZero AR9

Most picked next to it in real builds. Only parts our rules say fit the FailZero AR9 are listed.