A Stern 9mm upper pins onto the mil-spec AR-15 lower you already own. Add a MAG-AD9 magazine adapter and the rifle runs Glock 9mm magazines; add the MAG-ADMP9&40/P320 instead and it runs S&W M&P 9 or SIG P320 magazines. Your trigger, stock and optic stay where they are.
Every upper here comes assembled: a Stern 9mm barrel, a Glock-cut SD BU9 bolt, an assembled upper receiver with dust cover and forward assist, a handguard, a muzzle device and an SD CH1 charging handle. Barrel lengths run from 4 inches for a pistol build through 6, 8.5 and 10.5 inches, up to 16.1 inches for a carbine. Handguards come in M-LOK (MOD4 and MOD5) and KeyMod (MOD1 and MOD2).
Two things to check before you order. Your lower should be a mil-spec AR-15 or M16 pattern; billet lowers with irregular magwell contours are not recommended, and our compatibility page has the measurement to confirm yours. And run an H3 buffer, 5.4 ounces or heavier. The extra weight slows the bolt and extends the life of your components.
If you want the adapter and the upper matched and boxed together, see our 9mm conversion kits. Building your own upper? The 9mm barrels and bolts are sold on their own.
Not sure which adapter fits your magazines? Check the compatibility page first.