An M67 fragmentation grenade weighs 14 ounces. It is designed to mimic a baseball in general geometry. The average soldier is expected to be able to throw an M67 about 30 meters. The M67 is lethal at 5 meters, effective out to 15 meters, and dangerous up to 230 meters. It costs Uncle Sam around $45 apiece.
The minimum engagement range for an M224A1 60mm mortar is 70 meters. Light infantry units deploy 60mm mortars at the company level. Pushing these indirect fire weapons that far downinto the organizational system keeps their fires responsive. However, there yet remains a fair amount of dead space between organic company-level mortars and a hand-thrown grenade. In the years immediately following World War 2, American industry set out to address that. We naturally took our inspiration from the Germans.
40mm Grenade Launcher Origin Story
Ah, the Nazis. Bless their black shriveled hearts. They produced some of the most innovative war machines. We owe the modern assault rifle, the attack submarine, and the main battle tank to German wartime innovation. They also pioneered the technology required to produce a practical man-portable grenade launcher. That all started with a revolutionary type of propellant system.
Advertisement — Continue Reading Below
Physics is a cruel mistress. Mass times velocity in one direction will always equal mass times velocity in the other direction. That’s not just a good idea, that’s the law. What this means, practically speaking, is that tossing something that is heavy any significant distance will always produce a fair amount of recoil. The Germans mitigated this to a degree via the Hoch-und-Niederdruck system.
High & Low Pressure
Hoch-und-Niederdruck loosely translates to “High and Low Pressure.” The best way to appreciate the Hoch-und-Niederdruck system is to visualize a pressure vessel contained within a pressure vessel. High-pressure gases from the first chamber blow out a thin metal disk to vent into a second, larger chamber contained within the overall metallic shell. The resulting design produces a more gradual acceleration in comparison to more conventional weapons. Decreased acceleration spreads the recoil impulse out over time and equates to both less perceived recoil and larger potential payloads.
Advertisement — Continue Reading Below
Rocket launchers and similar recoilless systems consume enormous volumes of propellent. The Hoch-und-Niederdruck system was much more efficient. By incorporating dual-purpose shaped charge warheads with antipersonnel fragmentation effects, engineers produced a compact yet effective high explosive projectile that was small enough to be managed out of a handheld launcher. The resulting round covered that aforementioned dead space and gave the individual grenadier markedly more reach than he might have had with hand-thrown grenades alone.
The resulting round measured 40x46mm. Within these rounds, the two chambers function at 35,000 and 3,000 psi respectively. By comparison, the chamber pressure within a standard 7.62x51mm NATO round is closer to 60,000 psi.
Advertisement — Continue Reading Below
Now we needed something to shoot it. The program to develop America’s first man-portable grenade launcher with titled Project Niblick. In 1960, Project Niblick produced the M79.
The M79 — Big-Bore Rifled-Barrel Launcher
An unpretentious design, the M79 grenade launcher was a stubby break-open big-bore rifled-barrel weapon. The manual arms couldn’t have been more straightforward. It works just like your granddad’s old single-barrel rabbit gun. Thumb the barrel release lever right to open the action, drop in a round, close the action, slide off the safety, and squeeze the trigger. American GIs called the weapon the Thumper, Blooper, Bloop Tube, or Big Ed.
Advertisement — Continue Reading Below
The weapon’s maximum effective range was 400 meters against area targets and 150 meters against point targets like doors or windows. The M79 came with a complicated adjustable ladder sight. In the hands of an experienced grenadier, the M79 was remarkably accurate. With a little practice, a decent operator can throw those big fat grenades with surprising precision. As these relatively slow projectiles travel at a high arc, they can also be dropped behind cover from above. M79 grenade launchers were typically issued at the density of one per Infantry fire team or two per squad.
High Explosive Has Enter The Rooom
The effective casualty radius for today’s standard M433 HEDP (High Explosive Dual Purpose) rounds is five meters. First fielded in 1971, this dual-purpose warhead will also punch through two inches of steel armor plate at a 90-degree angle of incidence. The M433 HEDP round incorporates a brilliant spin-arming system that keeps the grenade inert until it has travelled a safe distance.
40mm High Explosive rounds move at the absolute glacial speed of 245 feet per second. The projectile is easily visualized in flight. It sports a rotational velocity of 37,000 rpm to the right. This rotation stabilizes the round while providing the centrifugal force needed to activate the spin arming system.
Advertisement — Continue Reading Below
Current-issue M433 rounds do not arm themselves until they have travelled about 30 meters.Vietnam-era 40mm grenades armed at between 14 and 27 meters. This spin-arming system is designed to help prevent grenadiers from injuring themselves if they engage a target that is too close.
Different 40mm Types
The Army developed two different types of close quarters 40mm rounds for use at intimate ranges. The first fired forty-five 10-grain steel flechettes. This was typically referred to as a beehive round based upon the buzzing sound it made when fired. 40mm flechette rounds were notoriously ineffective.
Advertisement — Continue Reading Below
Adopted in 1966, the M576E1 40mm buckshot round packed twenty 24-grain pellets. The M576E2 carried twenty-seven. At close ranges, these rounds performed swimmingly.
M781 training rounds sport a white nylon case and a fairly fragile blue plastic ogive cap. These rounds nicely mimic the trajectory of M433 HEDP rounds while producing a modest splash of orange powder on impact. We called them Cheetos back in the day.
The single-shot nature of the M79 left the grenadier vulnerable. Vietnam-era operators typically carried an M1911A1 handgun, but it was obvious that the system would work better if it was combined with a rifle. The result was the XM148. Colt called it the CGL4.
Synergy
Karl Lewis was a former Dayton, OH, police officer who answered a Colt challenge to develop a piggyback grenade launcher for the M16 rifle. Lewis took the project from idea to working prototype in a mere 47 days. He was actually a pretty fascinating guy. Lewis also developed the familiar interchangeable barrel Dan Wesson revolver and the Browning BLR lever-action rifle. In his free time, this same brilliant dude helped design the backpack oxygen system used by Apollo astronauts during their walks on the moon.
Lewis’ XM148 fit underneath a standard M16 rifle and incorporated an extended trigger assembly that was accessible without removing the firing hand from the pistol grip. However, this design was found to be susceptible to accidental discharges when operating in clingy jungle foliage. The XM148 therefore led to the definitive M203.
The Better Mousetrap
The underbarrel M203 fixed what was broken about the flawed XM148. A subset of the Special Purpose Individual Weapon (SPIW) program of the 1960s, the M203 was the only part of the SPIW enterprise to see production. Designed by the AAI Corporation, the M203 weighed three pounds unloaded and has seen service around the world.
First issued in 1969, the original M203 mounted underneath a standard M16A1 rifle and utilized a unique black polymer handguard. The handguard included a simple flip-up leaf sight graduated out to 250 meters that used the standard front post on the rifle. There was also a more precise pivoting quadrant sight affixed to the left aspect of the rifle’s carrying handle. This device had a flip-out front post and rear peep and was graduated to 400 meters.
To operate the M203 you press the left-sided latch and slide the barrel forward. Slip in a grenade and pull the barrel back to lock it in place. The safety is an ample pivoting tab located inside the trigger guard.
The extractor holds the spent case in place when the barrel is opened such that it falls clear of its own accord. The M203 works like a champ, but the sliding nature of the action limits the length of the rounds that may be fired. Some illumination ammunition in particular is quite long and will not fit. Modern M203’s can be mounted directly to the barrel or via a Picatinny interface. Grenade launcher considerations were the reason the heavy barrel on the M16A2 rifle was stepped down back behind the front sight base.
The German Solution
In 2009, the US Army adopted the German HK M320 to replace its M203. The M320 is a standalone weapon that can also be fitted underneath an M4 carbine, weighs 3.3 pounds and is a more versatile design.
The M320 loads via a side-pivoting barrel, so round length is no longer a factor. The gun includes a rugged double-action trigger and a folding front pistol grip. Performance is about the same as that of the M203.
Ruminations
Original M79’s are available as NFA (National Firearms Act) weapons, but they are just stupid expensive. Lewis Machine and Tool will gladly sell you a live M203. With a 40mm barrel installed, the weapon must be registered as a destructive device. The same gun moves as a conventional Title 1 rifle with a 37mm flare barrel instead.
Arms Unlimited sells the HK M320 with a 37mm barrel as a Title 1 firearm for $2,120. M433 HEDP rounds are legitimately unobtainable. However, there is lots of cool DIY 40mm fodder available online. While not the most practical weapon in civilian hands, a live 40mm grenade launcher will reliably make you some new friends at the local shooting range.
