Options abound, but boosting performance is a simple magazine swap away thanks to the new SureFire MAG5-60. It increases the number of rounds you can carry in the M400 to 60, making untimely reloads a thing of the past.
The MAG5-60 High-Capacity Magazine holds two, double-column stacks of 5.56 NATO rounds inside its mil-spec, hard-anodized aluminum body. To accommodate two stacks of cartridges, the lower portion of the MAG5-60 is wider than a conventional AR magazine, but it narrows toward the top to comply with STANAG 4179 specifications. Consequently, it fits in any AR-platform rifle that accepts STANAG mags. (For a detailed test of the SIG Sauer M400, go here.)
Internally, the MAG5-60 is anything but standard. A typical, polymer, double-column follower rides atop a coil spring that separates it from a larger, four-column follower. When rounds loaded into the magazine compress the spring between the two followers, the smaller nests inside the larger. The pair work together until the four-column follower reaches the tapered area of the magazine body, at which point the smaller of the two enters the narrowed section alone and lifts the remaining rounds to the feed lips. Beneath the four-column follower are two additional, much stiffer, coil springs joined by an aluminum cup that help raise the combined mass of five dozen rounds for reliable feeding.
All three coil springs compress around an elongated blade of aluminum, which is held in place by four tabs that wrap around the bottom of the magazine and secure the floorplate. Positioned upright in the magazine, the blade serves as a spring guide and a divider for the two double columns of cartridges, and it helps rounds transition from two stacks to one as they approach the top of the magazine's "shoulder."
As complicated as it may sound, the MAG5-60 is easy to disassemble, clean and put back together. The toughest part about assembly is getting the spring cup past the tabs on the bottom of the magazine. Most importantly, the additional components are simple and rugged, and they aid reliability rather than hindering it. American Rifleman Editor In Chief Mark Keefe and I have put more than 600 rounds through two MAG5-60 samples without experiencing a single issue that could be blamed on the magazine.
Granted, there are a couple tradeoffs to the increased capacity. The MAG5-60 is 1.75 inches longer than a standard 30-round magazine, and that extra length could become an issue when shooting prone or over a barricade. My sample tipped the scales at just a hair over 2 pounds when fully loaded with three boxes of Hornady 55-grain TAP FPD rounds—the same weight as two aluminum-bodied, 30-rounders loaded with the same ammo (but without a coupler joining them).
The MAG5-60's $129 price tag may cause sticker shock, but I know of no other AR magazine that offers such capacity in a truly practical size. And you can rest assured it exudes the quality for which SureFire is known. I dare you to dump one.Contact SureFire: (800) 828-8809; www.surefire.com