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The MOD.28 "Tromboncino" for the Carcano 91 TS Carbine: Great Idea, Imperfect Execution

By A. Wicks & G. Tansella

By the end of World War I, the composition and role of the infantry units in the Regio Esercito (literally: the Royal Army, the official name of the Italian army when Italy was a kingdom) had changed significantly since the outbreak of war. The watershed for the high command had been the Twelfth Battle of the River Isonzo.

The people that brought about these changes were the Germans, who had rushed to the aid of their Austro-Hungarian allies on the Alpine front. They had been extraordinarily successful with modestly sized infantry formations during the Tolmino offensive.

General Luddendorf in a speech held on 30 March 1918 had stated: “What counts is not the number of men, but the available firepower.” This brief phrase helps to understand the reasoning behind the introduction of the Carcano Model 28 grenade launcher, as well as the widespread distribution of light machine guns to infantry units.

The studies on producing a grenade launcher should not be viewed as an improvement in one specific area. But rather as part of the overall restructuring and modernisation of the army both regarding equipment, tactics, and structure of the army (size of individual armies, divisions, regiments, and even squads). Initially, the high command chose to take the French Armèe de Terre as a role model before going it alone from 1923 onwards.

Infantry units had to improve their flexibility both in terms of their offensive and defensive capabilities. This involved making the units train for a more mobile type of warfare, being able to quickly adapt to the terrain, and carry as much firepower as possible. Despite these efforts, they still remained about 15-years behind the German tactical thinking, which had already progressed to mechanized units up to divisional level.

There had been several studies carried out by worthy research and design firms and individuals like Perino, Cei-Rigotti, Revelli, and Marangoni. There were plenty of companies capable of manufacturing firearms using modern technology. However, none ever equipped the combat units apart from the odd minor exception.

The inevitable conclusion was drawn after hostilities were that two main points had to be quickly addressed in order to better prosecute a war: maneuverability and firepower. Therefore, a lot of effort was placed in designing close support weapons to lay down suppressive fire for both defence and attack, upgrading communications systems, creating mechanized infantry, self-propelled artillery and tank units.

THE MODEL 28 GRENADE LAUNCHER

The grenade launcher, combined with the carbine version of the Carcano 91 battlefield rifle, was a unique and complex piece of kit. The grenade was launched by firing the standard M91 ammunition with the round being blocked almost immediately by the inside base of the grenade launcher. The gas pressure was routed through four vents, launching the grenade.

It is essentially a hybrid system, part of which resembles the “Bertone” and “Benaglia” grenade launchers which were launched from the muzzle of a rifle and the Brixia 45mm “mortaio d’assalto” (assault mortar) which was used with mixed results between 1935 and 1943.

The Moschetto 91TS (moschetto=small musket, i.e. carbine) (Truppe Speciali – special troops) was a slightly modified version of the standard Moschetto 91. The Carcano 91TS was a bolt action carbine firing 6.5x52mm M91 ammunition; the six rounds were inserted into a clip which was then inserted into the body of the rifle. It had a 17.5-inch (445mm) long barrel with four grooves and a progressive rate of twist. The rounds weighed 162 grains, and the muzzle velocity was about 2,165 f/s (660m/s) with a maximum effective range of approximately 490-yards (450metres).

The carbine was in widespread use, but also outdated, although it remained in front line use until the end of World War II. Unbelievably, the cavalry version of the Moschetto 91/38 remained in military arsenals until the late sixties!

A lot of the following information has been extracted from an original “provisional” user manual, which is on display at the Museo della Guerra Bianca (Museum of the Great White War) in Adamello, Italy.

The grenade launching tube was positioned, rather unusually, on the right-hand side of the carbine because it used the carbine’s bolt, therefore, it could not be slung under the barrel as carbine’s trigger assembly, and magazine were in the way nor could it be placed on the left-hand side as it would have been impossible to operate the bolt. Placing it on top would have made aiming of either weapon impossible.

The grenade launcher was firmly attached to the carbine at two points. Additional support was given by a single sturdy bracket positioned at the launcher’s receiver/barrel interface, and the fore end of the stock grip of the carbine. Field-stripping the weapon involves notable effort and time. Attaching and detaching the grenade launcher is done by unscrewing the base of the magazine/trigger assembly to access the rear attaching bolt. The stock barrel cover is removed to access the attachment as well as releasing the bracket.

The five primary components of the grenade launcher are: the launcher itself, which is composed of a 38.5mm (1.52-inch) diameter smooth bore tube with an elastic retainer to keep the grenade in position when carrying the weapon “at the ready.”

The firing chamber which is almost cylindrical with a slight incline, to block the cartridge case as the round impacts the base of the grenade launcher tube. There are four divergent holes to allow the gas into the launch tube to propel the grenade which is simply resting on the tip of a rectangular shaped bolt (clearly visible in the photos). Firing the grenade is activated via a link lever from the carbine’s trigger mechanism.

Both the carbine and grenade launcher share the same bolt. The sights for both the carbine and the grenade launcher are mounted on the carbine, with the grenade launcher’s sights offset to the left when aiming (the carbines was dead center).

When ready to engage a target, the soldier would extract the bolt from the carbine by pulling the trigger and sliding out the bolt, then inserting it into the launcher’s receiver. To load, remove the safety device and insert the grenade into the launch tube so that it rests on the square protrusion at the base with the elastic retainer keeping it in place. Insert a cartridge, and fire it by pulling the carbine’s trigger. After firing, the expended cartridge case would be ejected as normal, and the round would fall through the port situated under the receiver.

THE GRENADE

The “tromboncino mod.28” launched grenades are much like a mortar round as the grenade itself had no propulsion system. The grenade also looks much like a mortar round as it just consisted of a warhead, casing, and four stabilizing fins at the rear. There were two different rounds: an inert one for training and one with a high explosive warhead with the official designation of “SR2.” The actual shape was almost identical to that of the Brixia 45mm mortar round although substantially smaller.

The rounds are about 4.5-inches (115mm) long with a 1.5-inch (38mm) diameter, which gives the round approximately 0.02 of an inch clearance in the tube. They weigh about 0.35-pounds (160grams). The actual round was made from a single block of metal with a safety device attached to the rounded head, which tapered down to the rear where four stabilizing tail fins were seated. The grenade only used impact detonation fuses. The warhead was placed in a cylindrical space and consisted of the explosive charge and spherical projectiles inserted into the inside walls of the warhead’s chamber. The lethal fragmentation radius was about 50-feet (15m) depending on the terrain, which is very similar to that of a hand-thrown assault grenade.

An inert grenade was used for training exercises and is reusable. The main difference between the exploding and inert grenades was that the inert one was just blued with the rear of the projectile not treated. Both grenades apparently had very similar ballistic properties with a stated maximum effective range of between about 327-feet and 655-feet (100m and 200m) with an absolute maximum range of just under 1050-feet! The sights only went up to 817-feet (250m).

Frequently, a weapon’s effectiveness, or potential effectiveness, is judged by theoretical data based on calculations, technical data and some tests. However, one should also bear in mind how the weapon was distributed throughout the armed forces. And how it was actually used in combat or failing that, how the infantry used it on exercise; whether it made tactical sense to have it. The Tromboncino was issued to one man in five or two for every rifleman squad.

In 1928, following the general shake-up of the army and tactics an infantry battalion was meant to be composed of five companies: Command was made up of three platoons: Command, Communications, and Scouts. Three rifle companies were divided into four platoons, one Command and three Rifle platoons. Each broken into three-fourteen man squads and a light machine gun squad comprising of fifteen men with two FIAT made LMGs. A Machine gun company was composed of one Command, and four heavy machine gun platoons, with three HMGs each. The tromboncino at our disposal belongs to the Arms Museum in Gardone Val Trompia whom we would like to thank for their time and generosity. We are, therefore, unable to draw any conclusions based on our own empirical evidence. However, a few general conclusions and ideas can be drawn.

The weapon is relatively heavy, and the center of mass is clearly tilted to the right which would make it rather awkward to carry. One receiver will also always be fully open would allow the elements, dirt, and vegetation to enter as it would not be sufficient to just cover the muzzle.

The lopsided weight distribution when “dry firing” both the carbine and grenade launcher quickly became quite uncomfortable, not to mention unstable. Cocking either weapon was also awkward because of the lack of balance. Carrying the weapon with a sling involves it moving a lot for the of lack of balance.

Aiming is difficult as the launch tube is heavy and set to the right. The weapon is aimed using the left rear sight which intuitively would point to a loss in accuracy.

The weapon that succeeded the “tromboncino” was the Brixia 45mm mortar, which also had numerous defects. This caused the High Command to reintroduce grenades launched from rifle muzzles by building the mod.43 under license from Germany (M43).

Finally, bearing in mind the very low effective distribution and operational lifespan of the tromboncino in the armed forces would lead one to conclude that the weapon was not considered to be satisfactory. There is no evidence that we could find that the tromboncino had ever seen combat.

The concept of increasing firepower for the infantry units was good. However, the actual design and distribution of the tromboncino were not up to standard.

This article first appeared in Small Arms Review V21N1 (January 2017)
and was posted online on November 18, 2016

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