To Thump or Not to Thump, That is the Question: M203 Grenade Launcher

The U.S. Army formally adopted the M79 Grenade Launcher in 1960 as a result of Project Niblick. The Thumper, Bloop Tube, or Blooper, as GIs came to call it, was a simple variation on the basic break open shotgun theme. The innovative low-recoil system that threw the M79’s 40mm grenades much farther than could be done with a pitching arm alone was itself an evolutionary development of the WWII-era German Hoch-und-Niederdruck System. This impressive amalgam of Teutonic verbiage translates roughly into High-Low Pressure System.

M203 Grenade Launcher

The Practical Tactical of the M203 Grenade launcher

The 40mm grenade fired from the M79 was specifically designed to cover the dead space between hand grenades and 60mm company mortars. These relatively low velocity projectiles travel in a high arc such that they can drop in vertically behind cover. The effective casualty radius for standard HEDP (High Explosive Dual Purpose) rounds is five meters and the warhead will burn through two inches of steel armor plate at a 90-degree angle of incidence.

Maximum effective range of this weapon is about 400 meters against area targets and 150 meters against point targets such as windows. Alternative rounds include smoke, buckshot, flechette, CS gas, less-than-lethal crowd control rounds, and illumination loads. All HE 40 mm rounds are spin armed such that they do not arm themselves until they have traveled about 30 meters out of the tube.

The Colt CGL4 or XM148 under-barrel grenade launcher was a single shot launch-er mounted underneath the barrel of a standard M16. This combination weapon was relatively effective but overly complicated and prone to accidental discharges when used in tangled jungle foliage. The subsequent type-classified M203 optimized the design.


The M203 weighs three pounds unloaded and is a robust and effective combat weapon used by dozens of the world’s militaries. Current M203A1 versions are designed to compliment the M4 family of carbines using a variation on the original mount. The M203A2 mounts via a standard forearm rail system. M203 barrels are available in 9 and 12-inch versions.

Tactical Obesity

The most desirable salient benefit of the modern small caliber assault rifle is its light weight. Today’s tactical rifles weigh a fraction of what their WWII counterparts did while delivering a markedly greater volume of fire. While the M203 does indeed add a substantial increase in man-portable firepower, the subsequent three-pound weight penalty is a big deal. With an M203 tacked on along with all the standard electronic ninja gear the previously thin and svelte M4A1 carbine can tip the scales at eleven pounds or more.

Modern warfare is frequently characterized by Military Operations in Urban Terrain (MOUT). MOUT operations involve room clearing and tactical maneuver within confined spaces such as alleys and stairwells. Under these circumstances the extra weight of the M203 can slow an operator down and contribute some undesirable extra fatigue to an already nerve-wracking job description.

The extra mass forward on the rifle aids in controllability but makes the rifle all the tougher to drive for long periods. While the addition of an indirect fire capability and some modest armor-piercing capability is indeed a proven combat multiplier, the maneuverability penalty in the dynamic and lethal world of modern combat is a serious consideration.

Using the M203 Grenade Launcher

The newest replacement for the M203 in the American military inventory is the German-made M320. Produced by the esteemed arms firm of Heckler and Koch, this versatile weapon can be readily run both on and off the host rifle. As a result this Information Age grenade launcher offers the best of both worlds.

A man-portable grenade launcher allows the individual operator to deliver accurate indirect fires as well as less than lethal rounds at a modest weight penalty. Given the extensive array of less than lethal options available for the 40mm platform many Law Enforcement agencies are gravitating toward this proven system.

The launcher is classified as a Destructive Device by the BATF and transfers the same way as a sound suppressor or short-barreled weapon. While a licensed Destructive Device dealer can be tough to find, BATF will allow conventional Class III dealers to transfer these launchers in small numbers infrequently. Lewis Machine and Tool is more than happy to sell these weapons to individuals and their website will get you started. Little adds more pizazz to a seasoned gun collection like a live grenade launcher.

Want to add a M203 to your rig? Think a bloop tube is worth it? Let us know in the comments.

11 Comments On This Article

  1. ATF Re-Classifies Certain Flares and 40mm Chalk Rounds as Explosives, Begins Confiscation

    Nick Leghorn

    July 28, 2015 135 comments



    The ATF is on a bit of a hit streak when it comes to random reclassifications. First they arbitrarily and capriciously changed their collective mind on the pistol stabilizing brace. Then they tried to ban M855 ammunition by branding it as “armor piercing.” Now it seems that they are turning their gaze upon some of the less common items and applying their similarly capricious thought processes. The latest targets are types of projectiles which can be fired from 40mm grenade launchers, specifically parachute flares and chalk practice rounds. And their ruling could soon be expanded to include all ammunition bigger than 1/2 inch in diameter . . .

    A thread on ARFCOM started it all, with the OP stating that they had been contacted by the ATF to turn in their recently purchased flare rounds. It is worth noting that these rounds had been previously classified by the ATF as non-explosives, but in this world of ever-changing definitions it seems that they have reversed themselves on that take.

    The logic they use to support their move (presented in a letter here and here) is that because the 40mm rounds in question are not “small arms” ammunition, the ATF can classify them as “low explosives” having no explosive properties whatsoever. This is also, of course, applicable to any ammunition with a diameter larger than 1/2 inch. That means firearms registered as a “destructive device” may soon have their own love note from the ATF classifying every round of ammo as a dangerous explosive that needs to be confiscated for the good of all humanity.

    President Obama has been looking for ways to manipulate the law to harass gun owners to the maximum extent possible for years, and this appears to be another attempt at instituting new gun control laws without the messiness of going through Congress. Today’s target are destructive device owners. There’s no telling who will be the next target of the President’s impotent rage against law-abiding citizens.

  2. Where is the rest of the very last sentence ? “Lewis Machine and Tool is more than happy to sell these weapons to individuals and …”

    • Hey, sorry about that! Looks like I missed a quotation mark in the formatting code, and that caused the whole last little bit to be cut off. Fixed now!
      Thanks for the heads up!

  3. I carry one for years and fire expert with both the Leaf Sight and Quad Sight. It will do in a pinch to keep the bad guys down. U.S.Army Infantry retired S.F.C. P.W.D.

  4. I carried one for years in several variants to the Cavalry squad, Platoon. The smoke and aerial illumination capabilities are outstanding. CQ

  5. The present weapon system is great for open terrain and their mobile infantry.
    The system is also well suited to garrison troop who do not have to hump over hill and dale.
    Small unit insertion teams, modern day assassination squads where hit and run is used find the extra security of both attack and defensive delaying if immefiate extraction is needed do mot mind extra weight.
    Also the milloons of non lrthal(sic.) Rounds within Homeland Security,police and private security, with incapacitating gas rounds, all to be used domesticly may well sabe the lszy from domestic disturbances.
    Do we civilians need them: of course we real men do.

  6. Question I was informed that the M203 was in fact a 38 mm flare launcher and the M204 was the 40mm grenad launcher used by the Army and Marine. The M203 38 mm was developed for the Navy. Was I miss informed?

    • Yes you were! The M203 is a 40mm grenade launcher. Now, this part is opinion, the 37mm launchers were produced for law enforcement and help ensure 40mm HE rounds don’t get used on civilians.

  7. @Johndeo is incorrect. The letter he refrences has poped up online from dubious sites. No ATF communications have indicated any sort restriction. Being a M203 owner I can say with 100% accuracy that the practice rounds are legal to purchase and use (at a federal level)

  8. As a scout sniper in the US Army, we NEVER left the wire without a M4/M203 as a break contact weapon. The combination of HEDP and CS/conventional smoke would cause chaos and confusion, and the launch point was difficult to detect, making it a great companion for our suppressed M110s. Later, I reclassed to special operations combat medic and I kept my M4/203! The smoke grenades allowed me to lay down my own concealment, to reach casualties in the open. I loved this system, and I only GRUDGINGLY switched to the M320, when I was forced to. It was so damn bulky, that using it on the rifle was nearly impossible, and the standalone stock added even more weight to a system that was already heavier than its predecessor. The M203 may have been replaced, but it will be missed, and for the record, I think they should be gone with the FN 40mm, rather than the HK. If I had the scratch, and could get ammo for a reasonable price, I wouldn’t hesitate to get one of these!