Run .45 ACP through the AR-15 lower you already have. A Stern .45 upper pins on with two takedown pins, and the MAG-ADMP45 adapter drops into a mil-spec magwell to feed S&W M&P 45 magazines. Large-frame Glock magazines in .45 ACP and 10mm are too wide for a mil-spec lower, which is why the .45 line is built around the M&P magazine.
Each upper comes assembled with a Stern .45 ACP barrel, a bottom-feed bolt, an assembled upper receiver, handguard, muzzle device and charging handle. Lengths cover the same range as our 9mm uppers: a 4-inch barrel for a pistol build, 6, 8.5 and 10.5 inches in between, and 16.1 inches for a carbine. Handguards are M-LOK on the MOD4 and MOD5 uppers and KeyMod on the MOD1 and MOD2.
Buffer weight matters more with .45 than with any other caliber we make. We recommend an 11-ounce buffer, and the 4-inch pistol uppers in particular should not be run on a standard carbine buffer. The 11 oz weighted buffer is sold on its own.
The adapter and upper are also sold together as a .45 ACP conversion kit, and .45 barrels are available for builders. Check the compatibility page before you order.