An American firm (Magpul) has developed a 40 round magazine for M-16 compatible 5.56mm assault rifles. The $23 polymer magazine has a larger transparent window strip to show how many rounds you have left. If successful in combat, the new magazine may spur the U.S. Army and Marine Corps to issue it, or a similar item, to the troops. This has happened before.
After years of being shown up by superior M-16 magazines from commercial firms, the U.S. Army recently began issuing an improved magazine of their own. Already, over half a million of the new magazines have been issued, mostly to troops in Iraq and Afghanistan, and those headed there. The oldest magazines are being turned in right away, and replaced by the new model. The new magazine is mainly designed to prevent jams when the round comes up from the magazine and into the firing chamber. This is accomplished with a new follower (a tab at the top of the magazine) design, as well as a new, corrosion resistant, spring.
But the new design is still behind some commercial designs, which are built mainly to keep the crud out. A big problem with the M-16 type rifle is that the fine sand and dust found in Iraq and Afghanistan can slip past the magazine and into the magazine well, and lead to a malfunction. So commercial firms have come out with several generations of magazines that try to seal the magazine well to keep the talcum powder like crud out of the rifle. For example, there is the Advanced Reliability Combat magazine, that includes a soft gasket that creates a dust proof seal when the magazine is inserted in an M-4, or similar weapon (like the SOCOM SCAR). These magazines cost $30 each (about 70 percent more than a standard magazine.) These high end magazines also, like the new army magazine, have better springs and a follower that minimizes jams. Troops will still buy commercial magazines, with their own money, just to be on the safe side.
The new Magpul 40 round magazine already has all these features, and many troops will buy them, if only to try them out.