Magtech First Defense Ammunition 300 AAC Blackout 123 Grain Full Metal Jacket

Last reviewed: 2026-04-18 by Jake Terry, FFL07/SOT3, NRA-certified firearms instructor.

The 300 Blackout 123 grain FMJ from Magtech First Defense runs supersonic at 2230 feet per second from a 16-inch barrel, delivering 1358 foot-pounds of muzzle energy. Built on boxer-primed brass cases with a non-corrosive powder charge, this load cycles reliably in AR-15 platforms chambered for 300 AAC Blackout and produces spent brass suitable for reloading. The full metal jacket bullet construction minimizes barrel fouling during extended training sessions and delivers consistent point-of-impact across lot numbers.

Performance at a Glance

Magtech manufactures every component in-house at its Brazilian facility, maintaining dimensional control over brass wall thickness, primer pocket depth, and bullet crimp tension. The 123-grain FMJ projectile seats to an overall cartridge length compatible with STANAG magazines and feeds through carbine-length gas systems without short-stroking. Supersonic velocity produces a distinct audible report and precludes the need for specialized subsonic bolt carrier groups or adjustable gas blocks.

This load ships in 50-round boxes and qualifies for standard ground shipping within the continental United States. All 300 Blackout ammo sold by Tatted Tacticals meets SAAMI pressure specifications and ships with manufacturer lot traceability.