From the Magpul press release:
In a move to enhance safety for responsible citizens, military, and law enforcement alike, Magpul Industries is now shipping the PMAG 40 GEN M3. Several years in the making, the PMAG 40 was delayed while GEN M3 technology was perfected to insure the highest quality product and full compatibility with the USMC M27 IAR. With the same compatibility as the 30-round GEN M3, the PMAG 40 provides 10 more rounds of capacity before requiring a reload—which could be a lifesaving difference. This new “safe capacity” offering is ideally suited for those who may need to respond to multiple threats without extra rifle magazines carried on their person, or for military members looking for an extra margin of safety in high-tempo operations. Just 2 1/8″ longer than the 30-round version, the PMAG 40 is just as reliable, durable, and compatible as the PMAG 30. The optimized magazine spring can handle feeding at cyclic rates over 1150 rounds per minute, so the extra 10 rounds of safety comes with the ability to more than keep up with platforms such as the M249 SAW and the M27 IAR. Designed for and tested in the most demanding environments. Available and suitable for all responsible civilian and military applications.
Available now from select retailers and distributors – they are already on the way to those locations today, with full production underway. Also, to beat the July 1st deadline for ownership in Colorado, a small portion of the first batch of PMAG 40s will be available from the Boulder Airlift Program for direct sale to CO residents, regardless of previous orders. Limit 2 per customer for direct sales.