Responding to user complaints, the U.S. Army has developed and successfully tested a new rear sight for the Mk19 40mm automatic grenade launcher. The Mk19 has been around for a long time, without much change. The iron rear sight was designed for older ammo, which caused the sight to be inaccurate. So users were more often just "walking in" exploding rounds to the target. That's because the old sight was not only inaccurate, but was always a hassle to use. The new sight solves most of the problems, and is cheaper (partly because it uses 27 fewer parts) and easier to maintain.
Meanwhile, the U.S. is considering replacing its 1960s era Mk19 40mm grenade launchers with a lighter and more effective Mk47 model. The replacement weapon is being tested in combat, while the army is still ordering new Mk19s. This is because the Mk19 gets the job done, is cheaper and the troops like it.
The Mk47 is lighter (18.2 kg/40 pounds) than the 35 kg (77 pound) Mk19. It is a little more compact, and has the electronic sighting and arming system which enables the gunner to determine the distance of the target (with a laser range finder), then push a button to have the weapon electronically program each shell, just before it is fired, for the number of seconds until the shell will explode, at the proper range from the gun, and above the enemy troops. If the time fuze does not work, the shell explodes when it hits something. The Mk47 can also operate like the Mk19, using "dumb" ammo that lacks the time fuze.
Both these 40mm weapons have a max range of 2,000 meters (and an effective range of about 1,500 meters). The Mk19 weapon, with a tripod, weighs 61.8 kg (136 pounds), while each 48 round magazine weighs 27.3 kg (60 pounds). The Mk19 effective rate of fire is about one round per second, and is usually fired in short (a few rounds) bursts of these 542 gram (19 ounce) grenades (which kill or incapacitate most people within six meters of the explosion and can wound at twice that).
The Mk19 is more complex than your usual machine-gun, expensive (about $20,000 each) and jams more frequently (once every thousand rounds, compared to once every 10,000 rounds for the M2 12.7mm machine-gun.). But it is reliable enough to remain popular and in demand. The lighter Mk47 costs about 50 percent more, and is about as reliable as the Mk19.
The U.S. Navy developed the Mk19 in the 1970s, for use on river and coastal patrol boats. The army adopted the weapon in the early 1980s, but it wasn't until the 1991 Gulf War that the Mk19 saw much action. Or at least some action. Users noted that the Mk19 was very effective out in the open, not so much in urban areas. In 2003, when the army and marines encountered much more combat out in the open, they found the Mk19 to be very valuable, more so than machine-guns.
What really makes the Mk47 different is the Mk285 40mm shells, each equipped with a time fuze. Normally only used in larger artillery shells, a time fuze in 40mm grenades makes it easier to get at enemy troops on roof tops or behind walls. These shells, which cost $213 each, can only be used with the Mk47. The first troops to get the Mk47 were U.S. NAVY SEALS, and other SOCOM troops.