The U.S. Army began replacing the M203 40mm grenade launcher with the M320 two years ago. To everyone's relief, the new version was a big success. The army even named the M320 ones of its top ten new systems for 2010.
The M203 fits under the barrel of the M16 rifle (and similar weapons) , and has been in use for forty years. The army is buying 71,000 of the new M320s (for about $3,500 each) to replace 50,000 M203s. The M320 is similar to the M203, but is easier to use, has its own pistol grip, is more accurate and can be used separately from an M16 with the addition of a stock.
The biggest improvement with the M320 is its sighting system, which features a laser range finder. At night, an infrared range finder enables a soldier wearing night vision goggles to see the light beam. In over a year of testing, the M320s sighting system was seen to make the weapon much more accurate than the older M203. This was particularly the case with new users. With the M203, you got better after you had fired a hundred or so rounds. That took time, and was expensive (the 40mm grenades cost about $28 each). The 40mm grenades weigh 545 grams (19 ounces) each and have a range of about 400 meters. The grenade explosion can kill within five meters, and wound up to ten meters or more.
What the U.S. actually did was adopt a version of the German designed AG36 40mm grenade launcher, as the M320. The British did the same, calling their version the L17A1.