Grenade Launchers: The Spigots

“Rifle grenades are regarded as the rifleman’s most reliable weapon against tanks, pill boxes, and exposed enemy personnel. At first, they may seem to be too small to d much damage, but their power is far greater than appearances would lead us to believe.”
Guidebook for Marines, Chapter 20, p.257 1951
Spigot-launched rifle grenades are a little bit better known than cup and rod grenades. Very occasionally they appear in movies. The best examples I can think of are in “Battle of the Bulge” and “From Russia With Love”.

The principle of a spigot launcher is very simple. Rather than fitting down a barrel the projectile has a tube that fits over the outside of the barrel. I have not encountered any examples of spigot launchers being used on rifles in the First World War. The principle was known at this time, since the Granatenwerfer 16 was an example of a spigot mortar.
When spigot grenades were introduced the rifles they were intended to be used with were not entirely suitable. Launching required an unobstructed length of barrel and a service rifle has structures such as bayonet lugs, foresights and woodwork in the way. The spigot launcher was therefore a length of tube that extended the barrel.
A number of spigot launchers for rifle grenades were in use in the Second World War.
The German example represents a very simple model of spigot launcher. It attaches using the bayonet lug and has a foresight for aiming grenades. The only projectile used was a 60mm hollow-charge anti-tank grenade.
The Japanese also made use of a spigot launcher. This was 15cm long and had a 27mm external diameter. It could be mounted on Type 38 6.5mm rifles. Two types of projectile were used. The fragmentation bomb was a Type 91 hand grenade with a tail unit screwed on. Range was around 110 yards with the grenade exploding once the 7-9 second fuse burned down. The smoke-screening bomb was a dedicated rifle grenade weighing 1.3 lb and using HC composition. The Japanese Navy developed a hollow-charge grenade with a 55 yd effective range and 40mm of penetration. Grenades were projected by a cartridge mounting a wooden bullet.
The British produced a spigot launcher for the No.4 rifle. Like many designs it had a flip up ladder sight. This was marked in increments of 25 yd from 25 to 100. The No.85 51mm anti-tank grenade (1.26lb) externally resembles the M9A1. The No.87 was a WP rifle grenade (1.25 lb). Post war, this launcher could also use the No.94 Energa anti-tank grenade. One man per platoon was issued the Energa as a replacement for the PIAT.

The US had four models of 22mm spigot launcher in use during World War Two. The M1 was for the M1903, the M2 for the M1917, the M7 for the M1 Garand and the M8 for the M1/M2 carbine. The M76 was introduced with the M14 in the 50s. The M7 was not issued until late 1943 and the development of the M8 had been held back until the M7 was ready. Prior to this American forces only used grenade launchers on bolt-action rifles. The Korean War-era Infantry Field Manual FM 7-10 (Ch.1, p.2) still states that a rifle squad is provided with one M1903 bolt-action Springfield for launching rifle-grenades.
The exterior of American grenade launchers have grooves or rings. These are graduations used in setting the range of a grenade. By varying how far down the tube the grenade is positioned pressure and launch velocity can be varied. When the launcher was used for high-angle fire some means of keeping the grenade at the desired graduation was needed. For the M1 (M1903) and M2 (M1917) launchers a separate clip was attached at the desired level. Several of these clips were packed with certain rifle grenade types. The M7 and M8 had a spring fitted near the launcher’s muzzle. This provided sufficient friction to keep the grenade in place until fired. Apparently these springs were very prone to breaking until the A2 modifications after the war.
If a grenade was fired from the semi-automatic Garand the bolt would unlock before the grenade was fully under way. This caused a drop in pressure and reduced grenade performance. The M7 included a mechanism to shut off the Garand’s gas system, keeping the breech closed. When fitted with a grenade launcher it was necessary to hand cycle the bolt after each shot. By the Korean war the M7A2/A3 launchers were in service. These had a modification so they only shut off the gas system when a grenade was being fired. It was no longer necessary to remove the launcher to have the rifle function semi-automatically. The M1/M2 carbine had a different mechanism and functioned semi-automatically with or without grenades.
Many armies teach soldiers to hold rifles with the butt underarm when firing grenades at low trajectories. The US Army manuals do not mention this and taught that grenade launchers could be fired from the shoulder. Helpfully, it does suggest the butt be well seated against the shoulder, the thumb held on the outside of the grip and the head well back from the sight. A body position where the body can move with the recoil was required. If prone the shoulder should not be used. Instead some means such as a rut in the earth be used. When firing from a foxhole the back wall of the trench could be used.

For high-angle fire the weapon was fired with the butt against the ground. A rubber recoil pad was available for the Garand. The carbine was held on its side so that both the heel and toe of the butt were in contact with the ground. The rifle or carbine was held at 30, 45 or 60 degrees and range adjusted by how far the grenade was slid down the spigot. Maximum range was increased by use of the “M7 Auxiliary Cartridge” (aka “Vitamin Pill”). This was a booster charge in what resembled (and may have been) a .45 Long Colt casing. The cartridge was inserted in the muzzle of the launcher before a grenade was fitted. The “Guidebook for Marines, 1951” cautions the auxiliary cartridge should not be used when shoulder firing due to “a tremendous wallop”. Use in the carbine was only for emergencies since the stock was not considered strong enough. Used of the vitamin pill was discontinued around 1954.

The different grenades had different ballistic behaviours, so for each there was a table showing which angle and “ring position” was required for a given range. 

A rotatable grenade sight (M15) with a spirit level could be fitted to the side of the stock. Interestingly, later field manuals for the M79 detail how M15 sights can be fitted to that weapon.

All grenades were fired by blank cartridges. This could be fiddly for the Garand. A cartridge was loaded directly into the breech (risking “Garand thumb” ) or the weapon unloaded and reloaded with a clip of blanks. Using a clip-loading mechanism the Garand magazine could not simply be topped up with blanks.
Blank cartridges for grenade projection are sometimes called “Ballistite” after the powder composition used in some examples. The term “ballistic” may also be encountered.

Ammunition for the American grenade launchers included:
M9/M9A1 (1.23 lb) 48mm hollow-charge anti-tank grenade. In a later war North Vietnamese forces used these fired from M44 Mosin-Nagan carbines.
M17 anti-personnel grenade. (1.47 lb) Mk2 “pineapple” grenade body with M9 rifle grenade tail. Impact fused.
M19 Smoke WP (1.5 lb). Screening, marking, anti-personnel and incendiary.
M20 Smoke HC. Screening smoke.
M22 Smoke Signalling. (1.26 lb) Emit coloured smoke for a minute after impact. Green, red, violet or yellow.
M23 Smoke streamer (1.16 lb). Before firing a section of tape on the nose must be removed to expose an air intake. Ten yards after launch produces a stream of smoke along its trajectory and for at least 12 seconds after firing. Green, red, violet or yellow. Maximum altitude Rifle: 155 yd in 11 sec, 203 yd in 12.4 sec with booster. Carbine: 97 yd in 8.5 sec, 133 yd in 10 sec with booster.
Parachute Flare. White, red, amber or green.
Five-star flare. White, red, amber or green.

M1-series Projection Adaptor. Tail unit for the Mk.2 hand grenade. A clip on one of the claws held the safety lever in position when the pin was removed. Firing causes the clip to setback and release the lever. Could also be used with the M34 WP grenade. Later model could be used with the M26 hand grenade. 0.38 lb plus grenade weight. WW2 60mm mortar warheads could also be thrown with this projector, for half the usual range. Later models of fuse will probably not arm if used this way.
M2-series Projection Adaptor. Tail unit for cylindrical, flat-bottomed grenades such as smoke, thermite, tear gas or the Mk3 offensive grenade.

During the Korean War it became apparent that something more potent than the M9A1 was needed. The US Army adopted the 75mm Energa grenade as the M28. A longer version of the M7, the M7A3, was introduced. The M28 was replaced by the M31, a 1.56 lb 66mm grenade of American origin. Performance of the two models is effectively the same, both giving around 200mm of penetration. 
High Trajectory Ranges:
M9A1 Rifle: 255 yd or 365 with booster. Carbine: 185 yd or 235 with booster. In theory it was possible for a high-angle shot to hit the thinner upper armour of a tank. In practice, the low velocity and wind effects made this difficult.
M17 Rifle: 200 yd, 290 with booster. Carbine: 135 yd.
Mk2 Frag in M1 adapter: Rifle: 180 yd or 225 with booster. Carbine: 130 yd.
Chemical grenade in M2 adapter: Rifle: 146 yd or 192 yd with booster. Carbine: 95 yd, 124 yd with booster.
M19/M20 Smoke grenades: Rifle: 215 yd or 310 with booster. Carbine: 150 yd or 215 with booster.
Flat Trajectory Ranges (up to 10 degrees elevation):
M9A1 Rifle: 104 yd or 175 yd with booster at 10 degrees. 215/315 at 25 degrees. Carbine: 70 yd at 10 degrees, 149 yd at 25 degrees. Time of flight about 25 yd in ½ second, 50 yd in 1¼ second. Lead for a target at 15 mph at 50 yd is 8 yd.
Mk.2 hand grenade in M1 adapter. Rifle: 50 yd in one second, 80 yd in 1.7 sec. Carbine: 39 yd in one second, 48 yd in 1.3 sec.
M17 Impact Frag. Rifle: 74 yds, Carbine: 51 yd.
While American soldiers were provided with grenade launchers and a wide range of ammunition types, it was noted in Infantry School Quarterly Vol.45-46, April 1956 p.82. “Rifle: grenades have long been a neglected and misused weapon, primarily because of misinterpretation and lack of information on their use. They are, however, the only antitank weapons of the rifle company other than the 3.5-inch rocket launchers. Not only are rifle grenades the antitank weapon of the rifle squad, they are also the squad’s “mortar” for indirect firing at area targets.”
A report on weapons use in the Korean War found no accounts of rifle grenades being used by US troops, although it did note there were incidences when they would have been useful. In all the units interviewed troops has thrown their grenade launchers away. The same report notes that the CCF (Communist Chinese Forces) did use grenade launchers. One wonders how many of these were items discarded by American troops!
While ingenious, the “ring and angle” range system does seem rather involved for a squad-level weapon that was intended to be used in close proximity to the enemy. In the trenches of Korea, grenade launchers may have been more effective if grouped into sections at platoon-level. Notable is that may other models of spigot launcher have rings or graduations, but do not appear to have a means of holding the grenade in a set position. This would not be the only instance of a piece of design being copied without understanding of function.
By the Vietnam-era the heavy M31 grenade was out of favour. It was not likely to perform adequately with the weaker 5.56mm ammunition and recoil would be even worse with the lighter M16. The M72 LAW and M79 seemed more promising. As is often its wont, disillusionment with one weapon caused the US Army to ignore the entire field. Potentially useful other types of rifle grenade were not made available to soldiers. For example, no adequate smoke screening round for the M79/M203 has ever been issued.
Some armies have remained enthusiastic users of rifle grenades. These include the Israelis, French, South Africans and Rhodesians. Belgium, Italy and China manufacture a range of models.
The Rhodesians often issued Energa grenades to the point man of a patrol, giving him RPG-level firepower during an encounter without the problems of back-blast and the added weight of a launcher. In a four-man Fire-force “stick” the two riflemen might each carry one or two rifle grenades.
The Rhodesians issued two cartridges for grenade projection. The full-power load (440 yd) was for high-angle fire with the butt against the ground. The reduced charge was for short-range (165 yd) “underarm” firing. It was considered a good joke to trick a comrade into firing the full-power load underarm or from the shoulder. It was prudent to keep your fingers out of the trigger guard and your thumb away from the pistol grip when firing grenades. The recoil could break them.
Using rifle grenades in semi-automatic rifles had introduced new complications. Propellant gases could escape from the opening breech or via the gas regulator. For many designs it was necessary to close the gas port to the barrel so the bolt could not cycle. The weapon needed to be manually cocked between each shot. On some designs the grenade sights are connected to the gas port. Flipping up the sight automatically closes the gas supply. Often a grenade cannot be placed fully over the muzzle if the grenade sights are not raised. Reloading the weapon with blank rounds was often slower with semi-automatics. Most self-loaders are not designed so that a magazine can be topped up with loose rounds while in position. The magazine needed to be removed, the chamber cleared and a new magazine of blanks inserted and a blank round chambered.
The original reason for the spigot launcher was that rifle barrels had not been designed with grenade launching in mind. This was to eventually change, and by the late 70s the latest designs of rifle had foresights not mounted at the muzzle and 22mm flash-hinders that also served as grenade spigots. Although assumed to be a “NATO standard” the common 22mm dimension was arrived at without official intervention. The various manufacturers emulated each other and were influenced by the rifle-grenades already in service.
The separate spigot launcher remained in use for some weapons. When creating the M14 from the Garand, the separate M76 launcher was developed rather than designing the flashhinder as an integral launcher. Some FAL rifles had integral launchers, while others (such as the British L1A1 SLR) required an attachment. The position of the SKS and AKM’s foresight required an add-on launcher for those nations that used rifle-grenades with these weapons. Below is a Polish example of an AK. External diameter of the launcher is 20mm. Many Yugoslavian SKS have grenade launchers. The Hungarian AMP-69 does not have a detachable spigot. Instead, the whole rifle has been reconfigured for grenade launching. A buffered stock and sliding fore-end help mitigate the effects of recoil. The gas tube is fitted with a cut-out.

As integral launchers became commonplace on military rifles spigot attachments became obsolete. Rifle grenades had not finished evolving, however. That is a story for another post.