A conversion kit is the two parts that turn your AR-15 into a 9mm carbine, matched and boxed together: a MAG-AD9 magazine adapter for the lower and a complete Stern Defense 9mm upper for the top, test fired before it ships. Drop the adapter into the magwell, pin on the upper, load a Glock magazine. Your lower, trigger, stock and optic do not change; the only components that change are the bolt and the barrel, and both come in the upper. To go back to 5.56, pull the adapter, swap the upper, and switch out the buffer.
Kits are named by the upper they include. The 4-inch M-LOK kit builds a pistol; the 16.1-inch kit builds a carbine; the 6, 8.5 and 10.5-inch kits sit in between. Handguard style is in the name as well, MOD4 and MOD5 for M-LOK, MOD1 and MOD2 for KeyMod.
The Key Components kits are for builders who already have an upper receiver and handguard. Each includes a Stern Defense 9mm barrel, an SD BU9 bolt and a MAG-AD9.
Use post-2004 Glock OEM magazines with the square notch for the best fit and function. Older U-notch magazines are not recommended, and Glock 26 and 27 magazines are too short for the adapter. Run an H3 buffer, 5.4 ounces or heavier. All three notes, and the lower-receiver check, are on our compatibility page.
Running S&W M&P or SIG P320 magazines instead of Glock? Order the upper from the 9mm uppers category and pair it with the MAG-ADMP9&40/P320 adapter. Install steps are in our install guide.