Soldier with a rifle-mounted M203 grenade launcher (as opposed to the M320)
American forces in Afghanistan have long complained of a significant drawback in their M203 rifle-mounted grenade launchers: enemies positioned behind the low, mud brick walls ubiquitous to the region's architecture could easily avoid incoming 40mm grenade rounds simply by ducking. You'd need a direct line of sight to enemy forces in order to inflict maximum damage. But not anymore.
Developed by a team of 11 researchers at the US Army's Armament Research, Development and Engineering Center at Picatinny Arsenal in New Jersey, these new 40mm counter-defilade rounds—dubbed the Small Arms Grenade Munitions (SAGM) are twice as effective (read: deadly) as conventional grenade rounds thanks to the addition of a fancy new proximity fuse that detonates while the round is still in the air, thereby raining shrapnel down on the enemy, even if he is hiding behind cover.
Work on the SAGM airburst round began in 2012 as a compliment to the Army's existing counter-defilade weapon, the XM25, which employs an on-board laser rangefinder to gauge distance to its target. "SAGM is complimentary to that; we are not competing against it," SAGM Project Officer Steven Gilbert said in a press statement. "The XM25 provides direct fire, SAGM is indirect."
"The SAGM cartridge, which is compatible with the Army's 40mm grenade launchers, provides the small-unit grenadier with a higher probability of achieving a first-shot kill against enemy personnel coupled with the ability to defeat personnel targets in defilade positions at increased ranges with greater accuracy and lethality," Gilbert continued.
Of course, the XM25's grenades had to be programmed prior to being fired—the grenadier had to input his rough distance from the enemy position, a value which was then transferred to the round's electronic fuse. The SAGM, on the other hand, can simply be loaded and fired without a second thought as its proximity fuse recognizes when its passed by a wall and immediately detonates on its own accord.
The new round is far from perfect, mind you. It obviously doesn't work against enemy forces hiding in buildings or under cover, nor is it particularly effective during close quarters combat—such as raids.
According to a Military.com report:
Door-kickers have also criticized the five-shot, 14-pound weapon system as being is more of a burden than a benefit to combat units. In March 2013, elements of 75th Ranger Regiment refused to take XM25 with them for a raid on a fortified enemy compound in Afghanistan, sources familiar with the incident said.
After an initial assessment, Ranger units found the XM25 too heavy and cumbersome for the battlefield. They were also concerned that the limited basic load of 25mm rounds was not enough to justify taking an M4A1 carbine out of the mission, sources say.