The Defcom launchers ALL have barrels that meet the U.S. D.O.D. requirements for material and rifling. The only launchers using steel
barrels are the high velocity like the MK 19. Low velocity grenade launchers i.e. M79, M203, XL200A1 are NOT closed breech weapons.

Please read the attached description from Picatinny Arsenal written in the late 1960″s.

40 MM WEAPON SYSTEM DATA SMUPA-DW5 PICATINNY ARSENAL
DOVER, NEW JERSEY

1. Standard 40 mm ammunition utilizes a unique HI-LOW pressure system to provide necessary muzzle velocity without undue recoil when fired from the shoulder. This system was primarily selected because the weapon does not have a sealed breech and the rounds are not obturated (Ordnance: to close (a hole or cavity) so as to prevent a flow of gas through it, esp. the escape of explosive gas from a gun tube during firing in the gun barrel.) The system as designed provides a
shot start and the round literally coasts through the barrel.

2. The cartridge case is a bi-chambered aluminum cup. It contains a press fit primer plug in its base, which seals a thick walled propellant retainer. This retainer holds a 0.127 mm (.005 inch) thick annealed brass propellant cup which contains approximately 365 milligrams (5.63280 grains) of M9 mortar propellant. The retainer contains six tapered vent holes equally spaced about the periphery. When struck by the firing pin, the primer ignites the propellant enclosed in the brass powder cup. The propellant burns creating a pressure of approximately 241,150 kPa (35,000 psi). This pressure ruptures the powder cup at the vent holes in the retainer allowing the propellant gases to expand into the low pressure chamber, the propellant gases, under a pressure of approximately 20,684 kPa (3,000 psi), propel the projectile into the lands of the gun barrel where a spin of approximately 3750 RPM is imparted at a muzzle velocity of 76.2 meters (276 feet per second).

2. It should be noted that the cartridge case is self-sustaining, i.e., the weapon sees little or NO propellant pressure. Pressure-time traces have indicated that peak pressure is reached in the low-pressure chamber between .1 and .2 milliseconds. Within one-half millisecond, the pressure is reduced to 3,447 kPa (500 psi) and within one millisecond the pressure has dropped to less than 689 kPa (100 psi). This data implies that by the time the base of the projectile has moved forward such that it is tangent to the leading edge of the cartridge case, the volume of space between the case and projectile has increased to the point where propellant pressure has been reduced, for all practical purposes, to zero.

3. The gun barrel contains six equally spaced rotating bands (rifling) to impart spin to the projectile. Tests to determine optimum barrel length established that only 152.4 mm (6 inches) of travel was required to provide necessary spin rate for projectile stability. The M79 has a barrel length of 355.6 mm (14 inches) and the M203 has a barrel length of 304.8 mm (12 inches). This length is provided primarily to permit hand support of the weapon and as a safety factor, to insure that the shooter, in holding the weapon, does not accidentally place his hand or fingers in front of the muzzle. ( That is called making it soldier proof)

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I hate grenades, but I love grenade launchers! Isn’t that weird?

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I do believe the original M-79 40mm grenade launcher had an aluminum barrel!

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Chalk practice rounds are more popular for this reason.

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If im dealing with explosive ordance I perfer a nice steel barrel to shoot it.

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I have seen pics of people firing what appear to be smoke rounds at shooting meets. Looks like fun but where can I get such ammo and how much (ballpark) is it?

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