Once more, the U.S. Army is looking at using caseless ammo, or ammo using plastic cartridges. Such a move would reduce ammo weight by about 20 percent. This makes a big difference to combat troops. Most of a nine man squads fire power come from its two 5.56mm machine-guns (M-249 SAW, or Squad Automatic Weapon). The 17.5 pound SAW normally uses a seven pound box magazine holding 200 rounds of ammo. The gunner usually carries three of these magazines into battle. Reducing ammo weight by 20 percent would save four pounds. This makes a difference, when you consider that the total weight a grunt is carrying comes to over 70 pounds (clothing, body armor, first aid kit, and lots of useful, or just mandatory, stuff.) 

Back in the 1980s, the German firm Dynamit Nobel developed a 4.73mm round that weighed much less than the existing 5.56mm rounds. The G11 assault rifle, designed to fire the caseless 4.73mm round, along with 510 rounds, weighed the same (16.2 pounds) as an M-16 with 240 rounds (eight, 30 round magazines.) The G11 normally carried 135 rounds (three 45 round magazines, one ready to fire, and two more on the weapon that could be in firing position within seconds.) With only two magazines installed, the G11 weighed 9.5 pounds. The West German army tested the G11 extensively in the late 1980s, and was considering adopting it, and its caseless ammo, to replace its 7.62mm assault rifles. But then the Cold War ended, Germany was united, and the decision was made to go with the cheaper G36 5.56mm weapon. The caseless ammo was also more expensive than the conventional 5.56mm stuff, and there were still concerns about reliability, even after years of testing. But now theres been another two decades of research on caseless ammo, and the stuff is being given another chance to show if it can compete with traditional rounds.