Had a change to look at these at SHOT and as with all things Surefire, they are well built, functional and a bit pricey.  Of course there's cheap and maybe it works and then there's what works and you pay for it to work.

The magazines come in two variants with 60 round or 100 round capacities. The original concept of a quad stack magazine is rooted in Soviet USSR small arms design.  Surefire is the first U.S. company to offer a reliably functional product. Drum magazines and similar super-high capacity magazines have existed for many years, but most models suffered from maintenance and reliability issues. The quad stack design addresses those issues while supporting a high rate of fire and reducing time spent reloading.

The 60 round Surefire High Capacity Magazine is only 8.7 inches in length, slimmer than two paired 30 round magazines, and has a loaded weight of 2.02 pounds. The 60 round variant will also fit into most dual magazine, molle mag pouches making it compatible with most current gear.

The United States Marine Corps made a recent decision to replace thousands of M249 SAW machine guns with heavy barreled HK416 variants. Reliable 60 round and 100 round magazines will keep Marines in the fight with a high rate of fire and longer sustained engagement.
Law Enforcement Agencies should also pay attention to these new products considering the increased number of active shooter situations they have encountered in recent years. 100 round magazines can be stowed in the trunks of patrol vehicles or in an officer’s go bag for use when things go bad. For the civilian firearm owner, the 60 and 100 round magazines may find a place in your 3-gun matches or in home defense.

Surefire described their new magazines as: “Constructed from Mil-Spec hard-anodized aluminum, they feed smoothly and reliably due to optimal geometry, non-binding coil springs, and ingenious nesting polymer followers. They require no lubricants and can be easily disassembled without tools for cleaning.”

TDS is currently accepting pre-orders and expect to able to begin shipping as soon as March 18th.  Military and LEO discount code will work for these items.